[Bug 2112552] [NEW] cat doesn't handle EPERM

[Skia]

Public bug reported:

This was found while investigating FTBFS in util-linux
(https://launchpadlibrarian.net/797485933/buildlog_ubuntu-questing-
amd64.util-linux_2.41-4ubuntu1_BUILDING.txt.gz).

This is triggered by this test: tests/ts/lsfd/mkfds-multiplexing
This test was skipped with GNU coreutils, because at some point, `cat` fails (with reason) to read a file: https://github.com/util-linux/util-linux/blob/35128888075ade600413092214b62acf3601ead9/tests/ts/lsfd/mkfds-multiplexing#L49-L55
With uutils coreutils, the test is not skipped, but fails for unclear reasons.

It boils down to this very easy reproducer: cat /proc/$$/syscall

GNU coreutils output:
skia at noble:/$ cat /proc/$$/syscall
cat: /proc/208/syscall: Operation not permitted
skia at noble:/$ echo $?
1

uutils coreutils output:
skia at questing:/$ cat /proc/$$/syscall
skia at questing:/$ echo $?
0

** Affects: rust-coreutils (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: util-linux (Ubuntu)
     Importance: Undecided
     Assignee: Skia (hyask)
         Status: New


** Tags: update-excuse

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https://bugs.launchpad.net/bugs/2112552

Title:
  cat doesn't handle EPERM

Status in rust-coreutils package in Ubuntu:
  New
Status in util-linux package in Ubuntu:
  New

Bug description:
  This was found while investigating FTBFS in util-linux
  (https://launchpadlibrarian.net/797485933/buildlog_ubuntu-questing-
  amd64.util-linux_2.41-4ubuntu1_BUILDING.txt.gz).

  This is triggered by this test: tests/ts/lsfd/mkfds-multiplexing
  This test was skipped with GNU coreutils, because at some point, `cat` fails (with reason) to read a file: https://github.com/util-linux/util-linux/blob/35128888075ade600413092214b62acf3601ead9/tests/ts/lsfd/mkfds-multiplexing#L49-L55
  With uutils coreutils, the test is not skipped, but fails for unclear reasons.

  It boils down to this very easy reproducer: cat /proc/$$/syscall

  GNU coreutils output:
  skia at noble:/$ cat /proc/$$/syscall
  cat: /proc/208/syscall: Operation not permitted
  skia at noble:/$ echo $?
  1

  uutils coreutils output:
  skia at questing:/$ cat /proc/$$/syscall
  skia at questing:/$ echo $?
  0

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