4.9-stable review patch. If anyone has any objections, please let me know.
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From: Arnd Bergmann arnd@arndb.de
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
--- fs/exec.c | 7 +++---- include/linux/sched.h | 6 +++++- 2 files changed, 8 insertions(+), 5 deletions(-)
--- a/fs/exec.c +++ b/fs/exec.c @@ -1228,15 +1228,14 @@ 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 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2999,7 +2999,11 @@ static inline void set_task_comm(struct { __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);