From: Jann Horn <jannh@xxxxxxxxxx> [ Upstream commit 06e62a46bbba20aa5286102016a04214bb446141 ] Before this change, if a multithreaded process forks while one of its threads is changing a signal handler using sigaction(), the memcpy() in copy_sighand() can race with the struct assignment in do_sigaction(). It isn't clear whether this can cause corruption of the userspace signal handler pointer, but it definitely can cause inconsistency between different fields of struct sigaction. Take the appropriate spinlock to avoid this. I have tested that this patch prevents inconsistency between sa_sigaction and sa_flags, which is possible before this patch. Link: http://lkml.kernel.org/r/20180702145108.73189-1-jannh@xxxxxxxxxx Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index 1b27babc4c78..9cf8add7038d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1417,7 +1417,9 @@ static int copy_sighand(unsigned long clone_flags, struct task_struct *tsk) return -ENOMEM; atomic_set(&sig->count, 1); + spin_lock_irq(¤t->sighand->siglock); memcpy(sig->action, current->sighand->action, sizeof(sig->action)); + spin_unlock_irq(¤t->sighand->siglock); return 0; } -- 2.17.1
