From 92347cfd62c174ab91ad97dd4bfbaa1d4aa28e67 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 8 Jun 2017 14:47:41 +0100 Subject: KEYS: fix refcount_inc() on zero If a key's refcount is dropped to zero between key_lookup() peeking at the refcount and subsequently attempting to increment it, refcount_inc() will see a zero refcount. Here, refcount_inc() will WARN_ONCE(), and will *not* increment the refcount, which will remain zero. Once key_lookup() drops key_serial_lock, it is possible for the key to be freed behind our back. This patch uses refcount_inc_not_zero() to perform the peek and increment atomically. Fixes: fff292914d3a2f1e ("security, keys: convert key.usage from atomic_t to refcount_t") Signed-off-by: Mark Rutland Signed-off-by: David Howells Cc: David Windsor Cc: Elena Reshetova Cc: Hans Liljestrand Cc: James Morris Cc: Kees Cook Cc: Peter Zijlstra Signed-off-by: James Morris --- security/keys/key.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/security/keys/key.c b/security/keys/key.c index cbae368c0e57..83da68d98b40 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -660,14 +660,11 @@ not_found: goto error; found: - /* pretend it doesn't exist if it is awaiting deletion */ - if (refcount_read(&key->usage) == 0) - goto not_found; - - /* this races with key_put(), but that doesn't matter since key_put() - * doesn't actually change the key + /* A key is allowed to be looked up only if someone still owns a + * reference to it - otherwise it's awaiting the gc. */ - __key_get(key); + if (!refcount_inc_not_zero(&key->usage)) + goto not_found; error: spin_unlock(&key_serial_lock); -- cgit v1.2.3