[PATCH v7 0/8] Improve the copy of task comm

[Yafang Shao]

Using {memcpy,strncpy,strcpy,kstrdup} to copy the task comm relies on the
length of task comm. Changes in the task comm could result in a destination
string that is overflow. Therefore, we should explicitly ensure the
destination string is always NUL-terminated, regardless of the task comm.
This approach will facilitate future extensions to the task comm.

As suggested by Linus [0], we can identify all relevant code with the
following git grep command:

  git grep 'memcpy.*->comm\>'
  git grep 'kstrdup.*->comm\>'
  git grep 'strncpy.*->comm\>'
  git grep 'strcpy.*->comm\>'

PATCH #2~#4:   memcpy
PATCH #5~#6:   kstrdup
PATCH #7~#8:   strcpy

Please note that strncpy() is not included in this series as it is being
tracked by another effort. [1]

In this series, we have removed __get_task_comm() because the task_lock()
and BUILD_BUG_ON() within it are unnecessary.

Suggested-by: Linus Torvalds <torvalds at linux-foundation.org>
Link: https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@mail.gmail.com/ [0]

Changes:
v6->v7:
- Improve the comment (Alejandro)
- Drop strncpy as it is being tracked by another effort (Justin)
  https://github.com/KSPP/linux/issues/90 [1]

v5->v6: https://lore.kernel.org/linux-mm/20240812022933.69850-1-laoar.shao@gmail.com/
- Get rid of __get_task_comm() (Linus)
- Use ARRAY_SIZE() in get_task_comm() (Alejandro)

v4->v5: https://lore.kernel.org/all/20240804075619.20804-1-laoar.shao@gmail.com/
- Drop changes in the mm/kmemleak.c as it was fixed by
  commit 0b84780134fb ("mm/kmemleak: replace strncpy() with strscpy()")
- Drop changes in kernel/tsacct.c as it was fixed by
  commmit 0fe2356434e ("tsacct: replace strncpy() with strscpy()")

v3->v4: https://lore.kernel.org/linux-mm/20240729023719.1933-1-laoar.shao@gmail.com/
- Rename __kstrndup() to __kmemdup_nul() and define it inside mm/util.c
  (Matthew)
- Remove unused local varaible (Simon)

v2->v3: https://lore.kernel.org/all/20240621022959.9124-1-laoar.shao@gmail.com/
- Deduplicate code around kstrdup (Andrew)
- Add commit log for dropping task_lock (Catalin)

v1->v2: https://lore.kernel.org/bpf/20240613023044.45873-1-laoar.shao@gmail.com/
- Add comment for dropping task_lock() in __get_task_comm() (Alexei)
- Drop changes in trace event (Steven)
- Fix comment on task comm (Matus)

v1: https://lore.kernel.org/all/20240602023754.25443-1-laoar.shao@gmail.com/

Yafang Shao (8):
  Get rid of __get_task_comm()
  auditsc: Replace memcpy() with strscpy()
  security: Replace memcpy() with get_task_comm()
  bpftool: Ensure task comm is always NUL-terminated
  mm/util: Fix possible race condition in kstrdup()
  mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}
  net: Replace strcpy() with strscpy()
  drm: Replace strcpy() with strscpy()

 drivers/gpu/drm/drm_framebuffer.c     |  2 +-
 drivers/gpu/drm/i915/i915_gpu_error.c |  2 +-
 fs/exec.c                             | 10 -----
 fs/proc/array.c                       |  2 +-
 include/linux/sched.h                 | 32 +++++++++++---
 kernel/auditsc.c                      |  6 +--
 kernel/kthread.c                      |  2 +-
 mm/util.c                             | 61 ++++++++++++---------------
 net/ipv6/ndisc.c                      |  2 +-
 security/lsm_audit.c                  |  4 +-
 security/selinux/selinuxfs.c          |  2 +-
 tools/bpf/bpftool/pids.c              |  2 +
 12 files changed, 65 insertions(+), 62 deletions(-)

-- 
2.43.5