object KMS is configured with auto-encryption,
there were issues when using docker registry -
this has been left unnoticed for a while.
This PR fixes an issue with compatibility.
Additionally also fix the continuation-token implementation
infinite loop issue which was missed as part of #9939
Also fix the heal token to be generated as a client
facing value instead of what is remembered by the
server, this allows for the server to be stateless
regarding the token's behavior.
- x-amz-storage-class specified CopyObject
should proceed regardless, its not a precondition
- sourceVersionID is specified CopyObject should
proceed regardless, its not a precondition
Just like GET/DELETE APIs it is possible to preserve
client supplied versionId's, of course the versionIds
have to be uuid, if an existing versionId is found
it is overwritten if no object locking policies
are found.
- PUT /bucketname/objectname?versionId=<id>
- POST /bucketname/objectname?uploads=&versionId=<id>
- PUT /bucketname/objectname?verisonId=<id> (with x-amz-copy-source)
- Implement a new xl.json 2.0.0 format to support,
this moves the entire marshaling logic to POSIX
layer, top layer always consumes a common FileInfo
construct which simplifies the metadata reads.
- Implement list object versions
- Migrate to siphash from crchash for new deployments
for object placements.
Fixes#2111
CopyObject was not correctly figuring out the correct
destination object location and would end up creating
duplicate objects on two different zones, reproduced
by doing encryption based key rotation.
Advantages avoids 100's of stats which are needed for each
upload operation in FS/NAS gateway mode when uploading a large
multipart object, dramatically increases performance for
multipart uploads by avoiding recursive calls.
For other gateway's simplifies the approach since
azure, gcs, hdfs gateway's don't capture any specific
metadata during upload which needs handler validation
for encryption/compression.
Erasure coding was already optimized, additionally
just avoids small allocations of large data structure.
Fixes#7206
some clients such as veeam expect the x-amz-meta to
be sent in lower cased form, while this does indeed
defeats the HTTP protocol contract it is harder to
change these applications, while these applications
get fixed appropriately in future.
x-amz-meta is usually sent in lowercased form
by AWS S3 and some applications like veeam
incorrectly end up relying on the case sensitivity
of the HTTP headers.
Bonus fixes
- Fix the iso8601 time format to keep it same as
AWS S3 response
- Increase maxObjectList to 50,000 and use
maxDeleteList as 10,000 whenever multi-object
deletes are needed.
size calculation in crawler was using the real size
of the object instead of its actual size i.e either
a decrypted or uncompressed size.
this is needed to make sure all other accounting
such as bucket quota and mcs UI to display the
correct values.
this is a major overhaul by migrating off all
bucket metadata related configs into a single
object '.metadata.bin' this allows us for faster
bootups across 1000's of buckets and as well
as keeps the code simple enough for future
work and additions.
Additionally also fixes#9396, #9394
enable linter using golangci-lint across
codebase to run a bunch of linters together,
we shall enable new linters as we fix more
things the codebase.
This PR fixes the first stage of this
cleanup.
This PR is to ensure that we call the relevant object
layer APIs for necessary S3 API level functionalities
allowing gateway implementations to return proper
errors as NotImplemented{}
This allows for all our tests in mint to behave
appropriately and can be handled appropriately as
well.
This PR allows setting a "hard" or "fifo" quota
restriction at the bucket level. Buckets that
have reached the FIFO quota configured, will
automatically be cleaned up in FIFO manner until
bucket usage drops to configured quota.
If a bucket is configured with a "hard" quota
ceiling, all further writes are disallowed.
global WORM mode is a complex piece for which
the time has passed, with the advent of S3 compatible
object locking and retention implementation global
WORM is sort of deprecated, this has been mentioned
in our documentation for some time, now the time
has come for this to go.
This commit fixes a performance issue caused
by too many calls to the external KMS - i.e.
for single-part PUT requests.
In general, the issue is caused by a sub-optimal
code structure. In particular, when the server
encrypts an object it requests a new data encryption
key from the KMS. With this key it does some key
derivation and encrypts the object content and
ETag.
However, to behave S3-compatible the MinIO server
has to return the plaintext ETag to the client
in case SSE-S3.
Therefore, the server code used to decrypt the
(previously encrypted) ETag again by requesting
the data encryption key (KMS decrypt API) from
the KMS.
This leads to 2 KMS API calls (1 generate key and
1 decrypt key) per PUT operation - while only
one KMS call is necessary.
This commit fixes this by fetching a data key only
once from the KMS and keeping the derived object
encryption key around (for the lifetime of the request).
This leads to a significant performance improvement
w.r.t. to PUT workloads:
```
Operation: PUT
Operations: 161 -> 239
Duration: 28s -> 29s
* Average: +47.56% (+25.8 MiB/s) throughput, +47.56% (+2.6) obj/s
* Fastest: +55.49% (+34.5 MiB/s) throughput, +55.49% (+3.5) obj/s
* 50% Median: +58.24% (+32.8 MiB/s) throughput, +58.24% (+3.3) obj/s
* Slowest: +1.83% (+0.6 MiB/s) throughput, +1.83% (+0.1) obj/s
```
This PR also tries to simplify the approach taken in
object-locking implementation by preferential treatment
given towards full validation.
This in-turn has fixed couple of bugs related to
how policy should have been honored when ByPassGovernance
is provided.
Simplifies code a bit, but also duplicates code intentionally
for clarity due to complex nature of object locking
implementation.
- Add conservative timeouts upto 3 minutes
for internode communication
- Add aggressive timeouts of 30 seconds
for gateway communication
Fixes#9105Fixes#8732Fixes#8881Fixes#8376Fixes#9028
this PR enforces md5sum verification for following
API's to be compatible with AWS S3 spec
- PutObjectRetention
- PutObjectLegalHold
Co-authored-by: Harshavardhana <harsha@minio.io>
Add dummy calls which respond success when ACL's
are set to be private and fails, if user tries
to change them from their default 'private'
Some applications such as nuxeo may have an
unnecessary requirement for this operation,
we support this anyways such that don't have
to fully implement the functionality just that
we can respond with success for default ACLs
Avoid GetObjectNInfo call from cache in CopyObjectHandler
- in the case of server side copy with metadata replacement,
the reader returned from cache is never consumed, but the net
effect of GetObjectNInfo from cache layer, is cache holding a
write lock to fill the cache. Subsequent stat operation on cache in
CopyObject is not able to acquire a read lock, thus causing the hang.
Fixes#8991
First step is to ensure that Path component is not decoded
by gorilla/mux to avoid routing issues while handling
certain characters while uploading through PutObject()
Delay the decoding and use PathUnescape() to escape
the `object` path component.
Thanks to @buengese and @ncw for neat test cases for us
to test with.
Fixes#8950Fixes#8647
- pkg/bucket/encryption provides support for handling bucket
encryption configuration
- changes under cmd/ provide support for AES256 algorithm only
Co-Authored-By: Poorna <poornas@users.noreply.github.com>
Co-authored-by: Harshavardhana <harsha@minio.io>
On every restart of the server, usage was being
calculated which is not useful instead wait for
sufficient time to start the crawling routine.
This PR also avoids lots of double allocations
through strings, optimizes usage of string builders
and also avoids crawling through symbolic links.
Fixes#8844
object lock config is enabled for a bucket.
Creating a bucket with object lock configuration
enabled does not automatically cause WORM protection
to be applied. PUT operation needs to specifically
request object locking or bucket has to have default
retention settings configured.
Fixes regression introduced in #8657
This is to ensure that when we have multiple tenants
deployed all sharing the same etcd for global bucket
should avoid listing each others buckets, this leads
to information leak which should be avoided unless
etcd is not namespaced for IAM assets in which case
it can be assumed that its a federated setup.
Federated setup and namespaced IAM assets on etcd
is not supported since namespacing is only useful
when you wish to separate the tenants as isolated
instances of MinIO.
This PR allows a new type of behavior, primarily
driven by the usecase of m3(mkube) multi-tenant
deployments with global bucket support.
This PR adds support below metrics
- Cache Hit Count
- Cache Miss Count
- Data served from Cache (in Bytes)
- Bytes received from AWS S3
- Bytes sent to AWS S3
- Number of requests sent to AWS S3
Fixes#8549
Currently, we use the top-level prefix "config/"
for all our IAM assets, instead of to provide
tenant-level separation bring 'path_prefix'
to namespace the access properly.
Fixes#8567
level - this PR builds on #8120 which
added PutBucketObjectLockConfiguration and
GetBucketObjectLockConfiguration APIS
This PR implements PutObjectRetention,
GetObjectRetention API and enhances
PUT and GET API operations to display
governance metadata if permissions allow.
- adding oauth support to MinIO browser (#8400) by @kanagaraj
- supports multi-line get/set/del for all config fields
- add support for comments, allow toggle
- add extensive validation of config before saving
- support MinIO browser to support proper claims, using STS tokens
- env support for all config parameters, legacy envs are also
supported with all documentation now pointing to latest ENVs
- preserve accessKey/secretKey from FS mode setups
- add history support implements three APIs
- ClearHistory
- RestoreHistory
- ListHistory
- add help command support for each config parameters
- all the bug fixes after migration to KV, and other bug
fixes encountered during testing.
specific errors, `application` errors or `all` by default.
console logging on server by default lists all logs -
enhance admin console API to accept `type` as query parameter to
subscribe to application/minio logs.
This commit removes the SSE-S3 key rotation functionality
from CopyObject since there will be a dedicated Admin-API
for this purpose.
Also update the security documentation to link to mc and
the admin documentation.
Fixes#7458Fixes#7573Fixes#7938Fixes#6934Fixes#6265Fixes#6630
This will allow the cache to consistently work for
server and gateways. Range GET requests will
be cached in the background after the request
is served from the backend.
- All cached content is automatically bitrot protected.
- Avoid ETag verification if a cache-control header
is set and the cached content is still valid.
- This PR changes the cache backend format, and all existing
content will be migrated to the new format. Until the data is
migrated completely, all content will be served from the backend.
When MinIO is behind a proxy, proxies end up killing
clients when no data is seen on the connection, adding
the right content-type ensures that proxies do not come
in the way.
This allows for canonicalization of the strings
throughout our code and provides a common space
for all these constants to reside.
This list is rather non-exhaustive but captures
all the headers used in AWS S3 API operations
This commit relaxes the restriction that the MinIO gateway
does not accept SSE-KMS headers. Now, the S3 gateway allows
SSE-KMS headers for PUT and MULTIPART PUT requests and forwards them
to the S3 gateway backend (AWS). This is considered SSE pass-through
mode.
Fixes#7753
This will allow cache to consistently work for
server and gateways. Range GET requests will
be cached in the background after the request
is served from the backend.
Fixes: #7458, #7573, #6265, #6630
When size is unknown and auto encryption is enabled,
and compression is set to true, putobject API is failing.
Moving adding the SSE-S3 header as part of the request to before
checking if compression can be done, otherwise the size is set to -1
and that seems to cause problems.
Most hadoop distributions hortonworks, cloudera all
depend on aws-sdk-java 1.7.x to 1.10.x - the releases
which have bugs related case sensitive check for
ETag header. Go changes the case of the headers set
to be canonical but only preserves them when set
through a direct map.
This fixes most compatibility issues we have had
in the past supporting older hadoop distributions.
CopyObject precondition checks into GetObjectReader
in order to perform SSE-C pre-condition checks using the
last 32 bytes of encrypted ETag rather than the decrypted
ETag
This also necessitates moving precondition checks for
gateways to gateway layer rather than object handler check
Prevents deferred close functions from being called while still
attempting to copy reader to snappyWriter.
Reduces code duplication when compressing objects.
Clients like AWS SDK Java and AWS cli XML parsers are
unable to handle on `\r\n` characters to avoid these
errors send XML header first and write white space characters
instead.
Also handle cases to avoid double WriteHeader calls
Currently, we were sending errors in Select binary format,
which is incompatible with AWS S3 behavior, errors in binary
are sent after HTTP status code is already 200 OK - i.e it
happens during the evaluation of the record reader.
Different gateway implementations due to different backend
API errors, might return different unsupported errors at
our handler layer. Current code posed a problem for us because
this information was lost and we would convert it to InternalError
in this situation all S3 clients end up retrying the request.
To avoid this unexpected situation implement a way to support
this cleanly such that the underlying information is not lost
which is returned by gateway.
This PR also adds some comments and simplifies
the code. Primary handling is done to ensure
that we make sure to honor cached buffer.
Added unit tests as well
Fixes#7141
- New parser written from scratch, allows easier and complete parsing
of the full S3 Select SQL syntax. Parser definition is directly
provided by the AST defined for the SQL grammar.
- Bring support to parse and interpret SQL involving JSON path
expressions; evaluation of JSON path expressions will be
subsequently added.
- Bring automatic type inference and conversion for untyped
values (e.g. CSV data).
This PR supports iam and bucket policies to have
policy variable replacements in resource and
condition key values.
For example
- ${aws:username}
- ${aws:userid}
When auto-encryption is turned on, we pro-actively add SSEHeader
for all PUT, POST operations. This is unusual for V2 signature
calculation because V2 signature doesn't have a pre-defined set
of signed headers in the request like V4 signature. According to
V2 we should canonicalize all incoming supported HTTP headers.
Make sure to validate signatures before we mutate http headers
Before this change the CopyObjectHandler and the CopyObjectPartHandler
both looked for a `versionId` parameter on the `X-Amz-Copy-Source` URL
for the version of the object to be copied on the URL unescaped version
of the header. This meant that files that had question marks in were
truncated after the question mark so that files with `?` in their
names could not be server side copied.
After this change the URL unescaping is done during the parsing of the
`versionId` parameter which fixes the problem.
This change also introduces the same logic for the
`X-Amz-Copy-Source-Version-Id` header field which was previously
ignored, namely returning an error if it is present and not `null`
since minio does not currently support versions.
S3 Docs:
- https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectCOPY.html
- https://docs.aws.amazon.com/AmazonS3/latest/API/mpUploadUploadPartCopy.html
When source is encrypted multipart object and the parts are not
evenly divisible by DARE package block size, target encrypted size
will not necessarily be the same as encrypted source object.
This PR adds pass-through, single encryption at gateway and double
encryption support (gateway encryption with pass through of SSE
headers to backend).
If KMS is set up (either with Vault as KMS or using
MINIO_SSE_MASTER_KEY),gateway will automatically perform
single encryption. If MINIO_GATEWAY_SSE is set up in addition to
Vault KMS, double encryption is performed.When neither KMS nor
MINIO_GATEWAY_SSE is set, do a pass through to backend.
When double encryption is specified, MINIO_GATEWAY_SSE can be set to
"C" for SSE-C encryption at gateway and backend, "S3" for SSE-S3
encryption at gateway/backend or both to support more than one option.
Fixes#6323, #6696
minio-java tests were failing under multiple places when
auto encryption was turned on, handle all the cases properly
This PR fixes
- CopyObject should decrypt ETag before it does if-match
- CopyObject should not try to preserve metadata of source
when rotating keys, unless explicitly asked by the user.
- We should not try to decrypt Compressed object etag, the
potential case was if user sets encryption headers along
with compression enabled.
This commit adds an auto-encryption feature which allows
the Minio operator to ensure that uploaded objects are
always encrypted.
This change adds the `autoEncryption` configuration option
as part of the KMS conifguration and the ENV. variable
`MINIO_SSE_AUTO_ENCRYPTION:{on,off}`.
It also updates the KMS documentation according to the
changes.
Fixes#6502
This PR implements one of the pending items in issue #6286
in S3 API a user can request CSV output for a JSON document
and a JSON output for a CSV document. This PR refactors
the code a little bit to bring this feature.
This refactor brings a change which allows
targets to be added in a cleaner way and also
audit is now moved out.
This PR also simplifies logger dependency for auditing
To conform with AWS S3 Spec on ETag for SSE-S3 encrypted objects,
encrypt client sent MD5Sum and store it on backend as ETag.Extend
this behavior to SSE-C encrypted objects.
This improves the performance of certain queries dramatically,
such as 'count(*)' etc.
Without this PR
```
~ time mc select --query "select count(*) from S3Object" myminio/sjm-airlines/star2000.csv.gz
2173762
real 0m42.464s
user 0m0.071s
sys 0m0.010s
```
With this PR
```
~ time mc select --query "select count(*) from S3Object" myminio/sjm-airlines/star2000.csv.gz
2173762
real 0m17.603s
user 0m0.093s
sys 0m0.008s
```
Almost a 250% improvement in performance. This PR avoids a lot of type
conversions and instead relies on raw sequences of data and interprets
them lazily.
```
benchcmp old new
benchmark old ns/op new ns/op delta
BenchmarkSQLAggregate_100K-4 551213 259782 -52.87%
BenchmarkSQLAggregate_1M-4 6981901985 2432413729 -65.16%
BenchmarkSQLAggregate_2M-4 13511978488 4536903552 -66.42%
BenchmarkSQLAggregate_10M-4 68427084908 23266283336 -66.00%
benchmark old allocs new allocs delta
BenchmarkSQLAggregate_100K-4 2366 485 -79.50%
BenchmarkSQLAggregate_1M-4 47455492 21462860 -54.77%
BenchmarkSQLAggregate_2M-4 95163637 43110771 -54.70%
BenchmarkSQLAggregate_10M-4 476959550 216906510 -54.52%
benchmark old bytes new bytes delta
BenchmarkSQLAggregate_100K-4 1233079 1086024 -11.93%
BenchmarkSQLAggregate_1M-4 2607984120 557038536 -78.64%
BenchmarkSQLAggregate_2M-4 5254103616 1128149168 -78.53%
BenchmarkSQLAggregate_10M-4 26443524872 5722715992 -78.36%
```
In many situations, while testing we encounter
ErrInternalError, to reduce logging we have
removed logging from quite a few places which
is acceptable but when ErrInternalError occurs
we should have a facility to log the corresponding
error, this helps to debug Minio server.
This commit adds key-rotation for SSE-S3 objects.
To execute a key-rotation a SSE-S3 client must
- specify the `X-Amz-Server-Side-Encryption: AES256` header
for the destination
- The source == destination for the COPY operation.
Fixes#6754
This PR adds support
- Request query params
- Request headers
- Response headers
AuditLogEntry is exported and versioned as well
starting with this PR.
Execute method in s3Select package makes a response.WriteHeader call.
Not calling it again in SelectObjectContentHandler function in case of
error in s3Select.Execute call.
On a heavily loaded server, getBucketInfo() becomes slow,
one can easily observe deleting an object causes many
additional network calls.
This PR is to let the underlying call return the actual
error and write it back to the client.
Current master didn't support CopyObjectPart when source
was encrypted, this PR fixes this by allowing range
CopySource decryption at different sequence numbers.
Fixes#6698
This PR fixes
- The target object should be compressed even if the
source object is not compressed.
- The actual size for an encrypted object should be the
`decryptedSize`
This commit fixes a wrong assignment to `actualPartSize`.
The `actualPartSize` for an encrypted src object is not `srcInfo.Size`
because that's the encrypted object size which is larger than the
actual object size. So the actual part size for an encrypted
object is the decrypted size of `srcInfo.Size`.
Without this fix we have room for two different type of
errors.
- Source is encrypted and we didn't provide any source encryption keys
This results in Incomplete body error to be returned back to the client
since source is encrypted and we gave the reader as is to the object
layer which was of a decrypted value leading to "IncompleteBody"
- Source is not encrypted and we provided source encryption keys.
This results in a corrupted object on the destination which is
considered encrypted but cannot be read by the server and returns
the following error.
```
<Error><Code>XMinioObjectTampered</Code><Message>The requested object
was modified and may be compromised</Message><Resource>/id-platform-gamma/
</Resource><RequestId>155EDC3E86BFD4DA</RequestId><HostId>3L137</HostId>
</Error>
```
CopyObject handler forgot to remove multipart encryption flag in metadata
when source is an encrypted multipart object and the target is also encrypted
but single part object.
This PR also simplifies the code to facilitate review.
This PR brings an additional logger implementation
called AuditLog which logs to http targets
The intention is to use AuditLog to log all incoming
requests, this is used as a mechanism by external log
collection entities for processing Minio requests.
This PR introduces two new features
- AWS STS compatible STS API named AssumeRoleWithClientGrants
```
POST /?Action=AssumeRoleWithClientGrants&Token=<jwt>
```
This API endpoint returns temporary access credentials, access
tokens signature types supported by this API
- RSA keys
- ECDSA keys
Fetches the required public key from the JWKS endpoints, provides
them as rsa or ecdsa public keys.
- External policy engine support, in this case OPA policy engine
- Credentials are stored on disks
The new call combines GetObjectInfo and GetObject, and returns an
object with a ReadCloser interface.
Also adds a number of end-to-end encryption tests at the handler
level.
* Revert "Encrypted reader wrapped in NewGetObjectReader should be closed (#6383)"
This reverts commit 53a0bbeb5b.
* Revert "Change SelectAPI to use new GetObjectNInfo API (#6373)"
This reverts commit 5b05df215a.
* Revert "Implement GetObjectNInfo object layer call (#6290)"
This reverts commit e6d740ce09.
This combines calling GetObjectInfo and GetObject while returning a
io.ReadCloser for the object's body. This allows the two operations to
be under a single lock, fixing a race between getting object info and
reading the object body.
This commit adds error handling for SSE-KMS requests to
HEAD, GET, PUT and COPY operations. The server responds
with `not implemented` if a client sends a SSE-KMS
request.
Add support for sse-s3 encryption with vault as KMS.
Also refactoring code to make use of headers and functions defined in
crypto package and clean up duplicated code.
When a S3 client sends a GET Object with a range header, 206 http
code is returned indicating success, however the call of the object
layer's GetObject() inside the handler can return an error and will lead
to writing an XML error message, which is obviously wrong since
we already sent 206 http code. So in the case, we just stop sending
data to the S3 client, this latter can still detect if there is no
error when comparing received data with Content-Length header
in the Get Object response.
Currently, requestid field in logEntry is not populated, as the
requestid field gets set at the very end.
It is now set before regular handler functions. This is also
useful in setting it as part of the XML error response.
Travis build for ppc64le has been quite inconsistent and stays queued
for most of the time. Removing this build as part of Travis.yml for
the time being.
With CoreDNS now supporting etcdv3 as the DNS backend, we
can update our federation target to etcdv3. Users will now be
able to use etcdv3 server as the federation backbone.
Minio will update bucket data to etcdv3 and CoreDNS can pick
that data up and serve it as bucket style DNS path.
This commit fixes the size calculation for multipart
objects. The decrypted size of an encrypted multipart
object is the sum of the decrypted part sizes.
Also fixes the key derivation in CopyObjectPart.
Instead of using the same object-encryption-key for each
part now an unique per-part key is derived.
Updates #6139
This commit fixes a weakness of the key-encryption-key
derivation for SSE-C encrypted objects. Before this
change the key-encryption-key was not bound to / didn't
depend on the object path. This allows an attacker to
repalce objects - encrypted with the same
client-key - with each other.
This change fixes this issue by updating the
key-encryption-key derivation to include:
- the domain (in this case SSE-C)
- a canonical object path representation
- the encryption & key derivation algorithm
Changing the object path now causes the KDF to derive a
different key-encryption-key such that the object-key
unsealing fails.
Including the domain (SSE-C) and encryption & key
derivation algorithm is not directly neccessary for this
fix. However, both will be included for the SSE-S3 KDF.
So they are included here to avoid updating the KDF
again when we add SSE-S3.
The leagcy KDF 'DARE-SHA256' is only used for existing
objects and never for new objects / key rotation.
This PR adds CopyObject support for objects residing in buckets
in different Minio instances (where Minio instances are part of
a federated setup).
Also, added support for multiple Minio domain IPs. This is required
for distributed deployments, where one deployment may have multiple
nodes, each with a different public IP.
- remove old bucket policy handling
- add new policy handling
- add new policy handling unit tests
This patch brings support to bucket policy to have more control not
limiting to anonymous. Bucket owner controls to allow/deny any rest
API.
For example server side encryption can be controlled by allowing
PUT/GET objects with encryptions including bucket owner.
This PR adds disk based edge caching support for minio server.
Cache settings can be configured in config.json to take list of disk drives,
cache expiry in days and file patterns to exclude from cache or via environment
variables MINIO_CACHE_DRIVES, MINIO_CACHE_EXCLUDE and MINIO_CACHE_EXPIRY
Design assumes that Atime support is enabled and the list of cache drives is
fixed.
- Objects are cached on both GET and PUT/POST operations.
- Expiry is used as hint to evict older entries from cache, or if 80% of cache
capacity is filled.
- When object storage backend is down, GET, LIST and HEAD operations fetch
object seamlessly from cache.
Current Limitations
- Bucket policies are not cached, so anonymous operations are not supported in
offline mode.
- Objects are distributed using deterministic hashing among list of cache
drives specified.If one or more drives go offline, or cache drive
configuration is altered - performance could degrade to linear lookup.
Fixes#4026
This is a trival fix to support server level WORM. The feature comes
with an environment variable `MINIO_WORM`.
Usage:
```
$ export MINIO_WORM=on
$ minio server endpoint
```
