[Bug 2001932] Autopkgtest regression report (glibc/2.31-0ubuntu9.11)

[Ubuntu SRU Bot]

All autopkgtests for the newly accepted glibc (2.31-0ubuntu9.11) for focal have finished running.
The following regressions have been reported in tests triggered by the package:

dune-common/2.6.0-4build1 (armhf)
khtml/5.68.0-0ubuntu1 (armhf)
kitemmodels/5.68.0-0ubuntu1 (armhf)
kpeople/5.68.0-0ubuntu1 (armhf)
kplotting/5.68.0-0ubuntu1 (armhf)
kpty/5.68.0-0ubuntu1 (armhf)
kxmlgui/5.68.0-0ubuntu2 (armhf)
linux-nvidia-tegra-5.15/5.15.0-1015.15~20.04.1 (arm64)
netplan.io/0.104-0ubuntu2~20.04.2 (s390x)
nfs-utils/1:1.3.4-2.5ubuntu3.4 (amd64)
ruby-stackprof/0.2.15-2 (arm64)
sbd/1.4.1-3 (s390x)
threadweaver/5.68.0-0ubuntu1 (armhf)


Please visit the excuses page listed below and investigate the failures, proceeding afterwards as per the StableReleaseUpdates policy regarding autopkgtest regressions [1].

https://people.canonical.com/~ubuntu-archive/proposed-
migration/focal/update_excuses.html#glibc

[1] https://wiki.ubuntu.com/StableReleaseUpdates#Autopkgtest_Regressions

Thank you!

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https://bugs.launchpad.net/bugs/2001932

Title:
  segfault in strncmp for avx2 at page boundaries

Status in GLibC:
  Fix Released
Status in glibc package in Ubuntu:
  Fix Released
Status in glibc source package in Focal:
  Fix Committed

Bug description:
  [Impact]

  Depending on size and location of the compared buffers in memory,
  particularly at the end of their respective pages, the AVX-2
  specialized code for strncmp has an off-by-one bug that can cause a
  segfault.

  See https://sourceware.org/bugzilla/show_bug.cgi?id=25933

  [Test case]

  > test_strncmp.c cat <<EOF
  #include <sys/mman.h>
  #include <string.h>
  #include <stdio.h>

  #define PAGE_SIZE 4096
  #define VEC_SIZE 32

  int main()
  {
  	int ret;
  	char *s1 = (char *)mmap(0, PAGE_SIZE*2, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  	char *s2 = (char *)mmap(0, PAGE_SIZE*2, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  	mprotect(s1+PAGE_SIZE, PAGE_SIZE, PROT_NONE);
  	mprotect(s2+PAGE_SIZE, PAGE_SIZE, PROT_NONE);
  	memset(s1, 'a', PAGE_SIZE);
  	memset(s2, 'a', PAGE_SIZE);
  	s1[PAGE_SIZE-1] = 0;
  	ret = strncmp(
              s1+PAGE_SIZE-VEC_SIZE*4-1,
              s2+PAGE_SIZE-VEC_SIZE*4,
              VEC_SIZE*4);
  	printf("strncmp returned %d\n", ret);
  	return ret;
  }
  EOF
  gcc -o test_strncmp test_strncmp.c
  ./test_strncmp
  # On buggy systems (e.g. mine), that last call segfaults

  [Regression potential]

  The fix could introduce another bug in the routine, and/or a
  performance regression.

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