4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
[ 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@google.com Signed-off-by: Jann Horn jannh@google.com Acked-by: Michal Hocko mhocko@suse.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Rik van Riel riel@redhat.com Cc: "Peter Zijlstra (Intel)" peterz@infradead.org Cc: Kees Cook keescook@chromium.org Cc: Oleg Nesterov oleg@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/kernel/fork.c +++ b/kernel/fork.c @@ -1109,7 +1109,9 @@ static int copy_sighand(unsigned long cl 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; }