Re: [PATCH v4 1/5] elfcore: use TASK_COMM_LEN instead of 16 in prpsinfo

From: Steven Rostedt
Date: Wed Oct 13 2021 - 09:11:13 EST


On Wed, 13 Oct 2021 10:23:42 +0000
Yafang Shao <laoar.shao@xxxxxxxxx> wrote:

> kernel test robot reported a -Wstringop-truncation warning after I
> extend task comm from 16 to 24. Below is the detailed warning:
>
> fs/binfmt_elf.c: In function 'fill_psinfo.isra':
> >> fs/binfmt_elf.c:1575:9: warning: 'strncpy' output may be truncated copying 16 bytes from a string of length 23 [-Wstringop-truncation]
> 1575 | strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> This patch can fix this warning.
>
> struct elf_prpsinfo was moved from include/uapi/linux/elfcore.h into
> include/linux/elfcore.h in commit
> 1e6b57d6421f ("unexport linux/elfcore.h")
>
> As it is not UAPI code, we can replace 16 with TASK_COMM_LEN without
> worrying about breaking userspace things.
>
> struct elf_prpsinfo is used to dump the task information in userspace
> coredump or kernel vmcore. So I verified what will happen to vmcore if
> I extend the size of TASK_COMM_LEN to 24. The result is that the vmcore
> still work fine as expected, for example:
>
> crash> ps
> PID PPID CPU TASK ST %MEM VSZ RSS COMM
> > 0 0 0 ffffffff8501a940 RU 0.0 0 0 [swapper/0]
> > 0 0 1 ffff996e00f81f80 RU 0.0 0 0 [swapper/1]
> > 0 0 2 ffff996e00f80000 RU 0.0 0 0 [swapper/2]
> > 0 0 3 ffff996e00f85e80 RU 0.0 0 0 [swapper/3]
> > 0 0 4 ffff996e00f83f00 RU 0.0 0 0 [swapper/4]
> 0 0 5 ffff996e00f8de80 RU 0.0 0 0 [swapper/5]
> > 0 0 6 ffff996e00f8bf00 RU 0.0 0 0 [swapper/6]
> > 0 0 7 ffff996e00f89f80 RU 0.0 0 0 [swapper/7]
> > 0 0 8 ffff996e00f88000 RU 0.0 0 0 [swapper/8]
> > 0 0 9 ffff996e00f93f00 RU 0.0 0 0 [swapper/9]
> > 0 0 10 ffff996e00f91f80 RU 0.0 0 0 [swapper/10]
> > 0 0 11 ffff996e00f90000 RU 0.0 0 0 [swapper/11]
> > 0 0 12 ffff996e00f95e80 RU 0.0 0 0 [swapper/12]
> > 0 0 13 ffff996e00f98000 RU 0.0 0 0 [swapper/13]
> > 0 0 14 ffff996e00f9de80 RU 0.0 0 0 [swapper/14]
> > 0 0 15 ffff996e00f9bf00 RU 0.0 0 0 [swapper/15]
>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> ---
> include/linux/elfcore-compat.h | 2 +-
> include/linux/elfcore.h | 4 ++--
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
> index e272c3d452ce..8a52a782161d 100644
> --- a/include/linux/elfcore-compat.h
> +++ b/include/linux/elfcore-compat.h
> @@ -43,7 +43,7 @@ struct compat_elf_prpsinfo
> __compat_uid_t pr_uid;
> __compat_gid_t pr_gid;
> compat_pid_t pr_pid, pr_ppid, pr_pgrp, pr_sid;
> - char pr_fname[16];
> + char pr_fname[TASK_COMM_LEN];
> char pr_psargs[ELF_PRARGSZ];
> };

Nice clean up, but should we add "#include <linux/sched.h>" to this header,
to make sure that it pulls in TASK_COMM_LEN define and not just hope it
gets pulled in beforehand by chance?

>
> diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
> index 2aaa15779d50..ff4e4e455160 100644
> --- a/include/linux/elfcore.h
> +++ b/include/linux/elfcore.h
> @@ -65,8 +65,8 @@ struct elf_prpsinfo
> __kernel_gid_t pr_gid;
> pid_t pr_pid, pr_ppid, pr_pgrp, pr_sid;
> /* Lots missing */
> - char pr_fname[16]; /* filename of executable */
> - char pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
> + char pr_fname[TASK_COMM_LEN]; /* filename of executable */
> + char pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */

This header is fine, as it pulls in sched/task_stack.h which includes
sched.h.

-- Steve

> };
>
> static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)