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Fix opam unable to find executables on systems where users belong to more than 32 groups when opam is built using musl libc #5381

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merged 4 commits into from
Sep 17, 2024
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Fix opam unable to find executables on systems where users belong to more than 32 groups when opam is built using musl libc #5381

merged 4 commits into from
Sep 17, 2024

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kit-ty-kate
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Details of the issue in musl described in https://www.openwall.com/lists/musl/2021/07/03/1
Fixes #5373

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dra27 commented Dec 6, 2022

I think there's a couple of bits in configure.ac from 5377b60#diff-49473dca262eeab3b4a43002adb08b4db31020d190caaad1594b47f1d5daa810 which also need reverting.

We should double-check that Unix.access doesn't regress either d6faa8d or 6f756ef (this is probably just a case of checking the Open Group POSIX docs... I'll be amazed if it regresses the first and quite surprised if it regresses the second!). It would be nice to check that the original bug being fixed in #4265, but that may be too tricky to set-up again.

@kit-ty-kate kit-ty-kate added this to the 2.2.0~alpha milestone Dec 7, 2022
@rjbou rjbou requested a review from dra27 December 7, 2022 17:56
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dra27 commented Dec 9, 2022

Annoying, Unix.access checks ruid and rgid rather than euid and egid (which is what exec will do). Ideally we therefore want to use faccessat with AT_EACCESS instead, which should be exactly equivalent to the present check, but without needing the libacl hackery for Cygwin (and, in fairness, any other Unix system which chooses to grant permissions with ACLs instead). However, that would cause opam to require C stubs for all builds, and I'm not so sure about that 🤷

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dra27 commented Dec 14, 2022

Discussed today: we decided we're not worried about requiring stubs in opam-core for all platforms, so wrapping faccessat should be fine, which we can then use instead of Unix.access. Happy for either of us to get to this - either way, we get rid of the libacl bindings!

@kit-ty-kate kit-ty-kate mentioned this pull request Dec 14, 2022
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@dra27 dra27 removed this from the 2.2.0~alpha milestone Jan 23, 2023
@kit-ty-kate kit-ty-kate force-pushed the unix-access branch 2 times, most recently from 2d6126b to 1f6ebf2 Compare July 8, 2024 21:13
@kit-ty-kate kit-ty-kate added this to the 2.3.0~alpha milestone Jul 8, 2024
@kit-ty-kate kit-ty-kate force-pushed the unix-access branch 4 times, most recently from 25f8b6c to d26ffce Compare September 8, 2024 14:56
@rjbou rjbou self-requested a review September 16, 2024 12:16
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Some format remarks : commits to squash, etc.
Also, commit messages are not very explicit, an update with more information could help.

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squashed

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Does doc/index.html need to be updated by the last commit (or others) ?

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Does doc/index.html need to be updated by the last commit

done. Feel free to squash if you're fine with the two last fixup commits

kit-ty-kate and others added 4 commits September 17, 2024 16:09
@kit-ty-kate
Remove the --with-acl option from the configure script
03a3dbb
@dra27 @kit-ty-kate
Use copy# where appropriate in dune files
3d283f9
@kit-ty-kate
resolve_command: Use faccessat instead of custom permission check
0e74798 
Unix.access uses RUID and RGID, which is not correct when doing a
PATH-search. The faccessat function is able to check permissions using
EUID and EGID instead. opam's hand-rolled check_permissions function is
therefore replaced with a binding for faccessat.

This simultaneously fixes two other things:
- Platforms (such as Cygwin) which use ACLs no longer need special
  support, because their implementations of faccessat already take ACLs
  into account
- We no longer use Unix.getgroups which means that we work around a
  problem with binaries built using musl libc and then used on systems
  where a user belongs to more than 32 groups
  (cf. https://www.openwall.com/lists/musl/2021/07/03/1)
@dra27 @kit-ty-kate
Move Windows stubs to opam-core
1e79693 
As opam now routinely has stubs, eliminate the complicated dances for
only linking stub libraries on Windows.
rjbou
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Thanks!

@kit-ty-kate kit-ty-kate merged commit 21bb251 into ocaml:master Sep 17, 2024
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kit-ty-kate pushed a commit to dra27/opam that referenced this pull request Sep 18, 2024
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release: Remove the getgroups workaround allowing users belonging to …
ac8a72d 
…more than 32 groups

Following the merge of ocaml#5381 this workaround is no longer needed
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opam init cannot find tools
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