exec: avoid gcc-8 warning for get_task_comm

commit 3756f6401c302617c5e091081ca4d26ab604bec5 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: cherry-pick stable linux-3.18.y commit 8b0673c3f698 for gcc 9 build]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I45c39936e1ae9ba78ed70165c687276ffd4f9cf3

diff --git a/fs/exec.c b/fs/exec.c
index b69705a87a0fc3e9eac16c2f90524ad6f7d703b2..036e69bf409fc00204e61add6f78c6e0a9006492 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1030,15 +1030,14 @@ 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

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 544355f6258bfe2ed0ad4a411b270415d42c4daa..f460bdec9ef788db2e25155a1284d6a1b364a722 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2491,7 +2491,12 @@ 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);