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authorDavid Howells <dhowells@redhat.com>2006-06-22 14:47:18 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-22 15:05:56 -0700
commit04c567d9313e4927b9835361d8ac0318ce65af6b (patch)
treed040ef59337342603f2cc30917493fb6a74a212a /Documentation/keys.txt
parentd720024e94de4e8b7f10ee83c532926f3ad5d708 (diff)
[PATCH] Keys: Fix race between two instantiators of a key
Add a revocation notification method to the key type and calls it whilst the key's semaphore is still write-locked after setting the revocation flag. The patch then uses this to maintain a reference on the task_struct of the process that calls request_key() for as long as the authorisation key remains unrevoked. This fixes a potential race between two processes both of which have assumed the authority to instantiate a key (one may have forked the other for example). The problem is that there's no locking around the check for revocation of the auth key and the use of the task_struct it points to, nor does the auth key keep a reference on the task_struct. Access to the "context" pointer in the auth key must thenceforth be done with the auth key semaphore held. The revocation method is called with the target key semaphore held write-locked and the search of the context process's keyrings is done with the auth key semaphore read-locked. The check for the revocation state of the auth key just prior to searching it is done after the auth key is read-locked for the search. This ensures that the auth key can't be revoked between the check and the search. The revocation notification method is added so that the context task_struct can be released as soon as instantiation happens rather than waiting for the auth key to be destroyed, thus avoiding the unnecessary pinning of the requesting process. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/keys.txt')
-rw-r--r--Documentation/keys.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/keys.txt b/Documentation/keys.txt
index 70302001270..3bbe157b45e 100644
--- a/Documentation/keys.txt
+++ b/Documentation/keys.txt
@@ -964,6 +964,16 @@ The structure has a number of fields, some of which are mandatory:
It is not safe to sleep in this method; the caller may hold spinlocks.
+ (*) void (*revoke)(struct key *key);
+
+ This method is optional. It is called to discard part of the payload
+ data upon a key being revoked. The caller will have the key semaphore
+ write-locked.
+
+ It is safe to sleep in this method, though care should be taken to avoid
+ a deadlock against the key semaphore.
+
+
(*) void (*destroy)(struct key *key);
This method is optional. It is called to discard the payload data on a key