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KEYS: load key flags and expiry time atomically in key_validate()

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In key_validate(), load the flags and expiry time once atomically, since
these can change concurrently if key_validate() is called without the
key semaphore held.  And we don't want to get inconsistent results if a
variable is referenced multiple times.  For example, key->expiry was
referenced in both 'if (key->expiry)' and in 'if (now.tv_sec >=
key->expiry)', making it theoretically possible to see a spurious
EKEYEXPIRED while the expiration time was being removed, i.e. set to 0.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers 2017-09-27 12:50:44 -07:00 committed by David Howells
parent 60ff5b2f54
commit 1823d475a5
1 changed files with 4 additions and 3 deletions
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7
security/keys/permission.c
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@ -88,7 +88,8 @@ EXPORT_SYMBOL(key_task_permission);
*/
int key_validate(const struct key *key)
{
unsigned long flags = key->flags;
unsigned long flags = READ_ONCE(key->flags);
time_t expiry = READ_ONCE(key->expiry);
if (flags & (1 << KEY_FLAG_INVALIDATED))
return -ENOKEY;
@ -99,9 +100,9 @@ int key_validate(const struct key *key)
return -EKEYREVOKED;
/* check it hasn't expired */
if (key->expiry) {
if (expiry) {
struct timespec now = current_kernel_time();
if (now.tv_sec >= key->expiry)
if (now.tv_sec >= expiry)
return -EKEYEXPIRED;
}