tree a71b454ba3ec9cd3b89b6f88301da3d45dfedb63
parent 17ced0ab7d9966627aeef19ae8e74fb109b788ab
author Marc Zyngier <maz@kernel.org> 1597853537 +0100
committer Luca Weiss <luca.weiss@fairphone.com> 1626347891 +0200

epoll: Keep a reference on files added to the check list

commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682 upstream.

When adding a new fd to an epoll, and that this new fd is an
epoll fd itself, we recursively scan the fds attached to it
to detect cycles, and add non-epool files to a "check list"
that gets subsequently parsed.

However, this check list isn't completely safe when deletions
can happen concurrently. To sidestep the issue, make sure that
a struct file placed on the check list sees its f_count increased,
ensuring that a concurrent deletion won't result in the file
disapearing from under our feet.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

(cherry picked from commit 9bbd20326fefd709dc6e7cbf7442ea640bb5f601)