[Bug 1850184] Re: losetup -f broken in 2.0.6-1ubuntu2

[Dimitri John Ledkov]

This is my replacement "minimized" losetup.c that exhibits the problem.

Simply, drop this into klibc sources
and run:

./debian/rules build; sudo ./usr/utils/static/losetup
1 Argc before find_unused_loop_devices()
0 Argc after find_unused_loop_devices()
Argc values before and after did not match.


Note that same source works fine as glibc binary:

gcc ./usr/utils/losetup.c; sudo ./a.out
1 Argc before find_unused_loop_devices()
1 Argc after find_unused_loop_devices()

** Attachment added: "losetup.c"
   https://bugs.launchpad.net/ubuntu/+source/klibc/+bug/1850184/+attachment/5301878/+files/losetup.c

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https://bugs.launchpad.net/bugs/1850184

Title:
  losetup -f broken in 2.0.6-1ubuntu2

Status in gcc-9 package in Ubuntu:
  New
Status in klibc package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Incomplete
Status in gcc-9 source package in Eoan:
  New
Status in klibc source package in Eoan:
  New
Status in linux source package in Eoan:
  Incomplete
Status in gcc-9 source package in Focal:
  New
Status in klibc source package in Focal:
  Fix Released
Status in linux source package in Focal:
  Incomplete

Bug description:
  [Impact]

   * sudo /usr/lib/klibc/bin/losetup -vf, which appears to be missbuilt,
  as main(argc) is reset to zero, after ioctl() operations in a function
  call, quite unexpectadly.

  [Test Case]

   * $ sudo /usr/lib/klibc/bin/losetup -vf
  Loop device is /dev/loop20
  loop: can't get info on device /dev/loop20: No such device or address

  is bad.

  Note that ioctl() must succeed, thus loop0 device must be configured
  to trigger the bug.

  
  [Regression Potential]

   * klibc is quite special, as it uses linux kernel headers/assembly.
  It seems like there is incompatibility between klibc sources, and
  gcc-9 with linux-5.3 when used to build userspace programmes.

   * disabling cf-protection and stack-clash-protection did not help.

   * building with gcc-8 does not exhibit the problem.

   * the workaround is quite simple in the code, keep a copy of argc to
  compare to it later in the code.

  [Other Info]

   * Original bug report

  http://autopkgtest.ubuntu.com/packages/c/casper/focal/amd64

  https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac
  /autopkgtest-focal/focal/amd64/c/casper/20191025_214555_df8b8@/log.gz

  ...
  [   11.751912] EXT4-fs (sda1): mounting ext2 file system using the ext4 subsystem
  [   11.761441] EXT4-fs (sda1): mounted filesystem without journal. Opts: (null)
  loop: can't get info on device /dev/loop1: No such device or address

  BusyBox v1.30.1 (Ubuntu 1:1.30.1-4ubuntu4) built-in shell (ash)
  Enter 'help' for a list of built-in commands.

  (initramfs) + mkdir result
  + set -x
  + read LINE
  + grep -e '^--OUT .* BEGIN-- .* --END--$' qemu-output.txt
  ++ grep -q /rofs result/lsblk.txt
  grep: result/lsblk.txt: No such file or directory
  autopkgtest [21:45:45]: test boot: -----------------------]
  autopkgtest [21:45:45]: test boot:  - - - - - - - - - - results - - - - - - - - - -
  boot                 FAIL non-zero exit status 2
  autopkgtest [21:45:45]: @@@@@@@@@@@@@@@@@@@@ summary
  boot                 FAIL non-zero exit status 2
  ...

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