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authorMark Rutland <mark.rutland@arm.com>2017-06-08 14:47:41 +0100
committerJames Morris <james.l.morris@oracle.com>2017-06-09 13:29:50 +1000
commit92347cfd62c174ab91ad97dd4bfbaa1d4aa28e67 (patch)
treeb3bc051f940ef773d5fb6e01401f70700ef8b875 /security
parent7cbe0932c2f2014d6e24e716e79ea3910b468950 (diff)
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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 <mark.rutland@arm.com> Signed-off-by: David Howells <dhowells@redhat.com> Cc: David Windsor <dwindsor@gmail.com> Cc: Elena Reshetova <elena.reshetova@intel.com> Cc: Hans Liljestrand <ishkamiel@gmail.com> Cc: James Morris <james.l.morris@oracle.com> Cc: Kees Cook <keescook@chromium.org> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
Diffstat (limited to 'security')
-rw-r--r--security/keys/key.c11
1 files 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);