8306882: (fs) Path.toRealPath(LinkOption.NOFOLLOW_LINKS) fails when "../../" follows a link

[bplb]

Modify Path.toRealPath such that it does not collapse links such as "link/.." or "link/../.." when LinkOption.NOFOLLOW_LINKS is specified or, in some cases, not.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8306882: (fs) Path.toRealPath(LinkOption.NOFOLLOW_LINKS) fails when "../../" follows a link (Bug - P4)

Reviewers

• Alan Bateman (@AlanBateman - Reviewer) ⚠️ Review applies to 75db4996

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/15397/head:pull/15397
$ git checkout pull/15397

Update a local copy of the PR:
$ git checkout pull/15397
$ git pull https://git.openjdk.org/jdk.git pull/15397/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 15397

View PR using the GUI difftool:
$ git pr show -t 15397

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/15397.diff

Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back bpb! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@bplb The following label will be automatically applied to this pull request:

• nio

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[bplb]

On Windows, the function GetFullPathName() does not access the file system and so is susceptible to collapsing links resulting in a path to a non-existent file. The path is examined to see whether it is one for which GetFullPathName would generate an incorrect result. If that is not the case, then GetFullPathName is used as before and there is no effective change. So this modification should affect only cases which would otherwise generate an incorrect result or fail.

[mlbridge]

Webrevs

• 03: Full - Incremental (1e1234d7)
• 02: Full (05a9cb9e)
• 01: Full - Incremental (75db4996)
• 00: Full (20dd8d49)

[turbanoff]

I suggest to extract code for this case to a separate method. sun.nio.fs.WindowsLinkSupport#getRealPath is already too big.

[bplb]

Sounds like a good idea.

[AlanBateman]

The changes to the Windows implementation of toRealPath(LinkOption.NOFOLLOW_LINKS) are going to take time to review.

Once suggestion that would help set the groundwork is to move the toRealPath tests to their own JUnit test. It's just historically that they were initially put in Misc.java. Also I think it would be useful to do the change to the Unix implementation separately, I think that needs a summary in the first place to understand why that change is needed.

[bplb]

Also I think it would be useful to do the change to the Unix implementation separately, I think that needs a summary in the first place to understand why that change is needed.

The issue was filed against the Unix implementation, so if the Unix implementation is separated from Windows then I think the Windows content should be moved to a new PR.

[bplb]

Once suggestion that would help set the groundwork is to move the toRealPath tests to their own JUnit test.

See JDK-8315241.

[bplb]

I think that [the Unix implementation] needs a summary in the first place to understand why that change is needed.

I can add a comment in the source, but here's some illustrative behavior using jshell. It uses some files as:

./dir/subdir
./aaa@ -> dir/subdir
./out.txt

and attempts to convert aaa/../../out.txt to a real path.

master

jshell> Path p = Path.of("aaa/../../out.txt")
p ==> aaa/../../out.txt

jshell> p.toRealPath()
$2 ==> /Users/bpb/dev/bugs/jdk/Path-toRealPath-8306882/out.txt                                        

jshell> p.toRealPath(LinkOption.NOFOLLOW_LINKS)
|  Exception java.nio.file.NoSuchFileException: /Users/bpb/dev/bugs/jdk/Path-toRealPath-8306882/aaa/out.txt
|        at UnixException.translateToIOException (UnixException.java:92)
|        at UnixException.rethrowAsIOException (UnixException.java:106)
|        at UnixException.rethrowAsIOException (UnixException.java:111)
|        at UnixPath.toRealPath (UnixPath.java:927)
|        at (#3:1)

As can be seen, when attempting to resolve the path without following links, the result is a non-existent file.

patch

jshell> Path p = Path.of("aaa/../../out.txt")
p ==> aaa/../../out.txt

jshell> p.toRealPath()
$2 ==> /Users/bpb/dev/bugs/jdk/Path-toRealPath-8306882/out.txt

jshell> p.toRealPath(LinkOption.NOFOLLOW_LINKS)
$3 ==> /Users/bpb/dev/bugs/jdk/Path-toRealPath-8306882/aaa/../../out.txt

Here the correct result is obtained.

[bplb]

The test and Windows changes reverted by 75db499 will be addressed by merging and modifying the patch #15474 and by a separate issue to be filed, respectively.

[AlanBateman]

I think looks okay, and I assume the work on converting the test to a standalone JUnit test will expand the test coverage to include this scenario.

[openjdk]

@bplb This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8306882: (fs) Path.toRealPath(LinkOption.NOFOLLOW_LINKS) fails when "../../" follows a link

Reviewed-by: alanb

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 1 new commit pushed to the master branch:

• 89d18ea: 8312018: Improve reservation of class space and CDS

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[bplb]

[...] I assume the work on converting the test to a standalone JUnit test will expand the test coverage to include this scenario.

It will, and the test will initially have to be excluded on Windows until JDK-8315273 is fixed.

[bplb]

/integrate

[openjdk]

Going to push as commit 63f561f.
Since your change was applied there have been 20 commits pushed to the master branch:

• 2436fb0: 8312306: Add more Reference.reachabilityFence() calls to the security classes using Cleaner
• 351c31e: 8315378: [BACKOUT] runtime/NMT/SummarySanityCheck.java failed with "Total committed (MMMMMM) did not match the summarized committed (NNNNNN)"
• c12ca88: 8312521: Unused field LocaleProviderAdapter#defaultLocaleProviderAdapter could be removed
• b38bcae: 8313656: assert(!JvmtiExport::can_support_virtual_threads()) with -XX:-DoJVMTIVirtualThreadTransitions
• c8acab1: 8315413: Remove special filtering of Continuation.yield0 in StackWalker
• ea5aa61: 8315383: jlink SystemModulesPlugin incorrectly parses the options
• 29ff1e4: 8315445: 8314748 causes crashes in x64 builds
• 145d8bc: 8315051: jdk/jfr/jvm/TestGetEventWriter.java fails with non-JVMCI GCs
• 486fa08: 8313873: java/nio/channels/DatagramChannel/SendReceiveMaxSize.java fails on AIX due to small default RCVBUF size and different IPv6 Header interpretation
• b0353ad: 8315242: G1: Fix -Wconversion warnings around GCDrainStackTargetSize
• ... and 10 more: https://git.openjdk.org/jdk/compare/dd64a4a483a831fd66912491af10502c4cf8596b...master

Your commit was automatically rebased without conflicts.

[openjdk]

@bplb Pushed as commit 63f561f.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.