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

[Yafang Shao]

On Wed, Oct 13, 2021 at 9:11 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> 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?
>

Sure, I will add it.
Thanks for the suggestion.

> >
> > 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)
>


-- 
Thanks
Yafang