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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 /security/keys/process_keys.c
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 'security/keys/process_keys.c')
-rw-r--r--security/keys/process_keys.c42
1 files changed, 26 insertions, 16 deletions
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index a50a91332fe..4d9825f9962 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -391,6 +391,8 @@ key_ref_t search_process_keyrings(struct key_type *type,
struct request_key_auth *rka;
key_ref_t key_ref, ret, err;
+ might_sleep();
+
/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
* searchable, but we failed to find a key or we found a negative key;
* otherwise we want to return a sample error (probably -EACCES) if
@@ -496,27 +498,35 @@ key_ref_t search_process_keyrings(struct key_type *type,
*/
if (context->request_key_auth &&
context == current &&
- type != &key_type_request_key_auth &&
- key_validate(context->request_key_auth) == 0
+ type != &key_type_request_key_auth
) {
- rka = context->request_key_auth->payload.data;
+ /* defend against the auth key being revoked */
+ down_read(&context->request_key_auth->sem);
- key_ref = search_process_keyrings(type, description, match,
- rka->context);
+ if (key_validate(context->request_key_auth) == 0) {
+ rka = context->request_key_auth->payload.data;
- if (!IS_ERR(key_ref))
- goto found;
+ key_ref = search_process_keyrings(type, description,
+ match, rka->context);
- switch (PTR_ERR(key_ref)) {
- case -EAGAIN: /* no key */
- if (ret)
+ up_read(&context->request_key_auth->sem);
+
+ if (!IS_ERR(key_ref))
+ goto found;
+
+ switch (PTR_ERR(key_ref)) {
+ case -EAGAIN: /* no key */
+ if (ret)
+ break;
+ case -ENOKEY: /* negative key */
+ ret = key_ref;
break;
- case -ENOKEY: /* negative key */
- ret = key_ref;
- break;
- default:
- err = key_ref;
- break;
+ default:
+ err = key_ref;
+ break;
+ }
+ } else {
+ up_read(&context->request_key_auth->sem);
}
}