[Bug 1874824] [NEW] pgrep reports error "cannot allocate" when run without stack limit

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You have been subscribed to a public bug by William Wilson (jawn-smith):

[Impact]

  - Users who have ulimit set high would see either slow
    or failed pgrep and pkill commands
  - Users who have ulimit set to unlimited would see
    failed pgrep and pkill commands
  - This bug occurs because the behavior of sysconf(_SC_ARG_MAX)
    changed with a newer version of the kernel.

[Test Case]

  - set the ulimit to unlimited by running `ulimit -S -s unlimited`
  - run `pgrep bash` to see that the "cannot allocate" error is
     printed and the command has failed.

[Where Problems Could Occur]

  - We have set upper and lower limits on the size of the malloc, but
    if further kernel versions break the call to sysconf in
    unexpected ways we could still see problems.

[Original Description]

If you have no stack limit (ulimit -S -s unlimited), any pgrep call will
fail with an error:

> pgrep vim
pgrep: cannot allocate 4611686018427387903 bytes

If you have a high stack limit (e.g. ulimit -S -s 500000), pgrep is very
slow:

> time pgrep vim
2196
real 8.48s user 8.40s syst 0.07s busy 99% rmem 253444

The relevant upstream bug report could be: https://gitlab.com/procps-ng/procps/-/issues/152
Archlinux bug report: https://bugs.archlinux.org/task/66093

procps:
  Installed: 2:3.3.16-1ubuntu2
  500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages

** Affects: procps (Ubuntu)
     Importance: Medium
     Assignee: William Wilson (jawn-smith)
         Status: Fix Released

** Affects: procps (Ubuntu Focal)
     Importance: Medium
     Assignee: William Wilson (jawn-smith)
         Status: In Progress

** Affects: procps (Ubuntu Groovy)
     Importance: Medium
     Assignee: William Wilson (jawn-smith)
         Status: In Progress

** Affects: procps (Ubuntu Hirsute)
     Importance: Medium
     Assignee: William Wilson (jawn-smith)
         Status: Fix Released

** Affects: procps (Debian)
     Importance: Unknown
         Status: New


** Tags: bitesize focal fr-1174 groovy hirsute patch
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pgrep reports error "cannot allocate" when run without stack limit
https://bugs.launchpad.net/bugs/1874824
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