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    SubjectRe: [PATCH v6 05/12] elfcore: make prpsinfo always get a nul terminated task comm
    On Mon, Oct 25, 2021 at 08:33:08AM +0000, Yafang Shao 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.
    >
    > Replacing strncpy() with strscpy_pad() can avoid this warning.
    >
    > This patch also replace the hard-coded 16 with TASK_COMM_LEN to make it
    > more compatible with task comm size change.
    >
    > I also verfied if it still work well when I extend the comm size to 24.
    > struct elf_prpsinfo is used to dump the task information in userspace
    > coredump or kernel vmcore. Below is the verfication of vmcore,
    >
    > crash> ps
    > PID PPID CPU TASK ST %MEM VSZ RSS COMM
    > 0 0 0 ffffffff9d21a940 RU 0.0 0 0 [swapper/0]
    > > 0 0 1 ffffa09e40f85e80 RU 0.0 0 0 [swapper/1]
    > > 0 0 2 ffffa09e40f81f80 RU 0.0 0 0 [swapper/2]
    > > 0 0 3 ffffa09e40f83f00 RU 0.0 0 0 [swapper/3]
    > > 0 0 4 ffffa09e40f80000 RU 0.0 0 0 [swapper/4]
    > > 0 0 5 ffffa09e40f89f80 RU 0.0 0 0 [swapper/5]
    > 0 0 6 ffffa09e40f8bf00 RU 0.0 0 0 [swapper/6]
    > > 0 0 7 ffffa09e40f88000 RU 0.0 0 0 [swapper/7]
    > > 0 0 8 ffffa09e40f8de80 RU 0.0 0 0 [swapper/8]
    > > 0 0 9 ffffa09e40f95e80 RU 0.0 0 0 [swapper/9]
    > > 0 0 10 ffffa09e40f91f80 RU 0.0 0 0 [swapper/10]
    > > 0 0 11 ffffa09e40f93f00 RU 0.0 0 0 [swapper/11]
    > > 0 0 12 ffffa09e40f90000 RU 0.0 0 0 [swapper/12]
    > > 0 0 13 ffffa09e40f9bf00 RU 0.0 0 0 [swapper/13]
    > > 0 0 14 ffffa09e40f98000 RU 0.0 0 0 [swapper/14]
    > > 0 0 15 ffffa09e40f9de80 RU 0.0 0 0 [swapper/15]
    >
    > It works well as expected.
    >
    > Reported-by: kernel test robot <lkp@intel.com>
    > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
    > Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    > Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
    > Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Steven Rostedt <rostedt@goodmis.org>
    > Cc: Al Viro <viro@zeniv.linux.org.uk>
    > Cc: Kees Cook <keescook@chromium.org>
    > Cc: Petr Mladek <pmladek@suse.com>
    > ---
    > fs/binfmt_elf.c | 2 +-
    > include/linux/elfcore-compat.h | 3 ++-
    > include/linux/elfcore.h | 4 ++--
    > 3 files changed, 5 insertions(+), 4 deletions(-)
    >
    > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
    > index a813b70f594e..a4ba79fce2a9 100644
    > --- a/fs/binfmt_elf.c
    > +++ b/fs/binfmt_elf.c
    > @@ -1572,7 +1572,7 @@ static int fill_psinfo(struct elf_prpsinfo *psinfo, struct task_struct *p,
    > SET_UID(psinfo->pr_uid, from_kuid_munged(cred->user_ns, cred->uid));
    > SET_GID(psinfo->pr_gid, from_kgid_munged(cred->user_ns, cred->gid));
    > rcu_read_unlock();
    > - strncpy(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));
    > + strscpy_pad(psinfo->pr_fname, p->comm, sizeof(psinfo->pr_fname));

    This should use get_task_comm().

    >
    > return 0;
    > }
    > diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
    > index e272c3d452ce..afa0eb45196b 100644
    > --- a/include/linux/elfcore-compat.h
    > +++ b/include/linux/elfcore-compat.h
    > @@ -5,6 +5,7 @@
    > #include <linux/elf.h>
    > #include <linux/elfcore.h>
    > #include <linux/compat.h>
    > +#include <linux/sched.h>
    >
    > /*
    > * Make sure these layouts match the linux/elfcore.h native definitions.
    > @@ -43,7 +44,7 @@ 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];
    > };
    >
    > diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
    > index 2aaa15779d50..8d79cd58b09a 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 */
    > };
    >
    > static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
    > --
    > 2.17.1
    >

    These structs are externally parsed -- we can't change the size of
    pr_fname AFAICT.

    --
    Kees Cook

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