linux-kernel - [PATCH] exec: avoid gcc-8 warning for get_task

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Date:   Mon,  4 Dec 2017 15:49:04 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <james.l.morris@...cle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] exec: avoid gcc-8 warning for get_task_comm

gcc-8 warns about using strncpy() with the source size as the limit:

fs/exec.c:1223:32: error: argument to 'sizeof' in 'strncpy' call is the same expression as the source; did you mean to use the size of the destination? [-Werror=sizeof-pointer-memaccess]

This is indeed slightly suspicious, as it protects us from source
arguments without NUL-termination, but does not guarantee that the
destination is terminated.

This changes it to strlcpy with a hardcoded length, to guarantee
a properly terminated string. Since we already use strlcpy() for
__set_task_comm(), the source should always be terminated properly,
so this patch won't change the behavior, but make it a bit more robust.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/exec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 6be2aa0ab26f..3e8012afe440 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1218,9 +1218,9 @@ static int de_thread(struct task_struct *tsk)

 char *get_task_comm(char *buf, struct task_struct *tsk)
 {
-	/* buf must be at least sizeof(tsk->comm) in size */
+	/* buf must be at least TASK_COMM_LEN in size */
 	task_lock(tsk);
-	strncpy(buf, tsk->comm, sizeof(tsk->comm));
+	strlcpy(buf, tsk->comm, TASK_COMM_LEN);
 	task_unlock(tsk);
 	return buf;
 }
-- 
2.9.0