signalfd: use wake_up_pollfree()

signalfd: use wake_up_pollfree()

commit 9537bae0da1f8d1e2361ab6d0479e8af7824e160 upstream.

wake_up_poll() uses nr_exclusive=1, so it's not guaranteed to wake up
all exclusive waiters.  Yet, POLLFREE *must* wake up all waiters.  epoll
and aio poll are fortunately not affected by this, but it's very
fragile.  Thus, the new function wake_up_pollfree() has been introduced.

Convert signalfd to use wake_up_pollfree().

Mot-CRs-fixed: (CR)
CVE-Fixed: CVE-2021-39698
Bug: 185125206

Change-Id: I203380553edf57ac23b249e18d937f2ec3c78671
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: d80e731ecab4 ("epoll: introduce POLLFREE to flush ->signalfd_wqh before kfree()")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20211209010455.42744-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Gajjala Chakradhar <gajjalac@motorola.com>
Reviewed-on: https://gerrit.mot.com/2197700
SME-Granted: SME Approvals Granted
SLTApproved: Slta Waiver
Tested-by: Jira Key
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.com>
Submit-Approved: Jira Key
(cherry picked from commit e6c52d9f3ac2c2af5678ba583dd223d97dca2afe)