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exec: avoid gcc-8 warning for get_task_comm

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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 keeps the strncpy() to ensure we have properly padded target
buffer, but ensures that we use the correct length, by passing the
actual length of the destination buffer as well as adding a build-time
check to ensure it is exactly TASK_COMM_LEN.

There are only 23 callsites which I all reviewed to ensure this is
currently the case.  We could get away with doing only the check or
passing the right length, but it doesn't hurt to do both.

Link: http://lkml.kernel.org/r/20171205151724.1764896-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Kees Cook <keescook@chromium.org>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Aleksa Sarai <asarai@suse.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Arnd Bergmann 2017-12-14 15:32:41 -08:00 committed by Linus Torvalds
parent 302ec300ef
commit 3756f6401c
2 changed files with 8 additions and 5 deletions
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7
fs/exec.c
View file

@ -1216,15 +1216,14 @@ killed:
return -EAGAIN;
}
char *get_task_comm(char *buf, struct task_struct *tsk)
char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
{
/* buf must be at least sizeof(tsk->comm) in size */
task_lock(tsk);
strncpy(buf, tsk->comm, sizeof(tsk->comm));
strncpy(buf, tsk->comm, buf_size);
task_unlock(tsk);
return buf;
}
EXPORT_SYMBOL_GPL(get_task_comm);
EXPORT_SYMBOL_GPL(__get_task_comm);
/*
* These functions flushes out all traces of the currently running executable

6
include/linux/sched.h
View file

@ -1503,7 +1503,11 @@ static inline void set_task_comm(struct task_struct *tsk, const char *from)
__set_task_comm(tsk, from, false);
}
extern char *get_task_comm(char *to, struct task_struct *tsk);
extern char *__get_task_comm(char *to, size_t len, struct task_struct *tsk);
#define get_task_comm(buf, tsk) ({ \
BUILD_BUG_ON(sizeof(buf) != TASK_COMM_LEN); \
__get_task_comm(buf, sizeof(buf), tsk); \
})
#ifdef CONFIG_SMP
void scheduler_ipi(void);