avoid spurious POLLIN returns in signalfd

The new code in kernel/signal.c does not allow fetching private signals
from another task.  This patch avoid spurious POLLIN returns from a
signalfd poll(2) operation.

Signed-off-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/signalfd.c b/fs/signalfd.c
index f1da89203a9a..3b07f26d984d 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -133,7 +133,8 @@ static unsigned int signalfd_poll(struct file *file, poll_table *wait)
          * the peer disconnects.
          */
         if (signalfd_lock(ctx, &lk)) {
-                if (next_signal(&lk.tsk->pending, &ctx->sigmask) > 0 ||
+                if ((lk.tsk == current &&
+                     next_signal(&lk.tsk->pending, &ctx->sigmask) > 0) ||
                     next_signal(&lk.tsk->signal->shared_pending,
                                 &ctx->sigmask) > 0)
                         events |= POLLIN;