fs/binfmt_elf: replace open-coded string copy with get_task_comm

It is better to use get_task_comm() instead of the open coded string
copy as we do in other places.

struct elf_prpsinfo is used to dump the task information in userspace
coredump or kernel vmcore.  Below is the verification 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.

Some comments are added to explain why we use the hard-coded 16.

Link: https://lkml.kernel.org/r/20211120112738.45980-5-laoar.shao@gmail.com
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.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: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index f8c7f26..b9a33cc 100644 (file)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1585,7 +1585,7 @@ 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));
+       get_task_comm(psinfo->pr_fname, p);
 
        return 0;
 }

diff --git a/include/linux/elfcore-compat.h b/include/linux/elfcore-compat.h
index e272c3d..54feb64 100644 (file)
--- a/include/linux/elfcore-compat.h
+++ b/include/linux/elfcore-compat.h
@@ -43,6 +43,11 @@ 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;
+       /*
+        * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
+        * changed as it is exposed to userspace. We'd better make it hard-coded
+        * here.
+        */
        char                            pr_fname[16];
        char                            pr_psargs[ELF_PRARGSZ];
 };

diff --git a/include/linux/elfcore.h b/include/linux/elfcore.h
index 957ebec..746e081 100644 (file)
--- a/include/linux/elfcore.h
+++ b/include/linux/elfcore.h
@@ -65,6 +65,11 @@ struct elf_prpsinfo
        __kernel_gid_t  pr_gid;
        pid_t   pr_pid, pr_ppid, pr_pgrp, pr_sid;
        /* Lots missing */
+       /*
+        * The hard-coded 16 is derived from TASK_COMM_LEN, but it can't be
+        * changed as it is exposed to userspace. We'd better make it hard-coded
+        * here.
+        */
        char    pr_fname[16];   /* filename of executable */
        char    pr_psargs[ELF_PRARGSZ]; /* initial part of arg list */
 };