linux-kernel - [PATCH v4 1/5] elfcore: use TASK_COMM

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Date:   Wed, 13 Oct 2021 10:23:42 +0000
From:   Yafang Shao <laoar.shao@...il.com>
To:     keescook@...omium.org, rostedt@...dmis.org, peterz@...radead.org,
        pmladek@...e.com, viro@...iv.linux.org.uk,
        akpm@...ux-foundation.org, valentin.schneider@....com,
        mathieu.desnoyers@...icios.com, qiang.zhang@...driver.com,
        robdclark@...omium.org, christian@...uner.io,
        dietmar.eggemann@....com, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, davem@...emloft.net, kuba@...nel.org
Cc:     linux-kernel@...r.kernel.org, Yafang Shao <laoar.shao@...il.com>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH v4 1/5] elfcore: use TASK_COMM_LEN instead of 16 in prpsinfo

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@...el.com>
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Petr Mladek <pmladek@...e.com>
---
 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];
 };
 
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 */
 };
 
 static inline void elf_core_copy_regs(elf_gregset_t *elfregs, struct pt_regs *regs)
-- 
2.17.1