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8306882: (fs) Path.toRealPath(LinkOption.NOFOLLOW_LINKS) fails when "../../" follows a link #15397

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@bplb bplb commented Aug 23, 2023

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.


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

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👋 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 openjdk bot added the rfr Pull request is ready for review label Aug 23, 2023
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@bplb The following label will be automatically applied to this pull request:

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bplb commented Aug 23, 2023

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.

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// to determine whether this would occur, and if so use the
// full path manually derived in the process.
String fullpath = null;
if (path.contains("..")) {
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I suggest to extract code for this case to a separate method. sun.nio.fs.WindowsLinkSupport#getRealPath is already too big.

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Sounds like a good idea.

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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.

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bplb commented Aug 28, 2023

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.

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bplb commented Aug 29, 2023

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

See JDK-8315241.

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bplb commented Aug 29, 2023

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.

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bplb commented Aug 29, 2023

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.

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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.

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@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

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

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bplb commented Aug 30, 2023

[...] 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 bplb requested a review from AlanBateman August 30, 2023 20:10
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bplb commented Aug 31, 2023

/integrate

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openjdk bot commented Aug 31, 2023

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.

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@bplb Pushed as commit 63f561f.

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@bplb bplb deleted the Path-toRealPath-8306882 branch September 22, 2023 21:32
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