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

[William Wilson]

Robie,

pgrep and pkill are sharing the same code. Essentially pkill runs pgrep
and then issues a kill signal to the resulting pid. Therefore this fix
applies to both pkill and pgrep. Additionally, the source of the problem
comes from the behavior of `sysconf(_SC_ARG_MAX)` changing in newer
kernels. This function call only exists in one place in the procps
codebase, so no other commands are affected by the same issue.

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https://bugs.launchpad.net/bugs/1874824

Title:
  pgrep reports error "cannot allocate" when run without stack limit

Status in procps package in Ubuntu:
  Fix Released
Status in procps source package in Focal:
  In Progress
Status in procps source package in Groovy:
  In Progress
Status in procps source package in Hirsute:
  Fix Released
Status in procps package in Debian:
  New

Bug description:
  [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      changed with a newer version of the kernel.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

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