sysrq: Fix possible race with exiting task

sysrq should grab the tasklist lock, otherwise calling force_sig() is
not safe, as it might race with exiting task, which ->sighand might be
set to NULL already.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 7867b7c4538e..a1bcad7ef739 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -322,11 +322,13 @@ static void send_sig_all(int sig)
 {
         struct task_struct *p;
 
+        read_lock(&tasklist_lock);
         for_each_process(p) {
                 if (p->mm && !is_global_init(p))
                         /* Not swapper, init nor kernel thread */
                         force_sig(sig, p);
         }
+        read_unlock(&tasklist_lock);
 }
 
 static void sysrq_handle_term(int key)