CVE Request -- kernel: epoll: can leak file descriptors when returning -ELOOP

[Petr Matousek <pmatouse () redhat com>]

An epoll_ctl(,EPOLL_CTL_ADD,,) operation can return '-ELOOP' to prevent
circular epoll dependencies from being created.  However, in that case
we do not properly clear the 'tfile_check_list'.

An unprivileged local user could use this flaw to crash the system.

Regression introduced via 28d82dc1c4edbc352129f97f4ca22624d1fe61de
commit.

Upstream fix:
13d518074a952d33d47c428419693f63389547e9

References:
https://lkml.org/lkml/2012/3/27/65
https://lkml.org/lkml/2012/4/17/247
https://bugzilla.redhat.com/show_bug.cgi?id=837502

Thanks,
-- 
Petr Matousek / Red Hat Security Response Team