tree 7255c489175110780706a7eaf04fe8f0f34611b5
parent 66f71da9dd38af17dc17209cdde7987d4679a699
author Eric Biggers <ebiggers@google.com> 1545986083 -0800
committer Linus Torvalds <torvalds@linux-foundation.org> 1546027907 -0800

userfaultfd: convert userfaultfd_ctx::refcount to refcount_t

Reference counters should use refcount_t rather than atomic_t, since the
refcount_t implementation can prevent overflows, reducing the
exploitability of reference leak bugs.  userfaultfd_ctx::refcount is a
reference counter with the usual semantics, so convert it to refcount_t.

Note: I replaced the BUG() on incrementing a 0 refcount with just
refcount_inc(), since part of the semantics of refcount_t is that that
incrementing a 0 refcount is not allowed; with CONFIG_REFCOUNT_FULL,
refcount_inc() already checks for it and warns.

Link: http://lkml.kernel.org/r/20181115003916.63381-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>