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Subject[PATCH 3.12 79/88] KEYS: potential uninitialized variable
From: Dan Carpenter <>

3.12-stable review patch. If anyone has any objections, please let me know.


commit 38327424b40bcebe2de92d07312c89360ac9229a upstream.

If __key_link_begin() failed then "edit" would be uninitialized. I've
added a check to fix that.

This allows a random user to crash the kernel, though it's quite
difficult to achieve. There are three ways it can be done as the user
would have to cause an error to occur in __key_link():

(1) Cause the kernel to run out of memory. In practice, this is difficult
to achieve without ENOMEM cropping up elsewhere and aborting the

(2) Revoke the destination keyring between the keyring ID being looked up
and it being tested for revocation. In practice, this is difficult to
time correctly because the KEYCTL_REJECT function can only be used
from the request-key upcall process. Further, users can only make use
of what's in /sbin/request-key.conf, though this does including a
rejection debugging test - which means that the destination keyring
has to be the caller's session keyring in practice.

(3) Have just enough key quota available to create a key, a new session
keyring for the upcall and a link in the session keyring, but not then
sufficient quota to create a link in the nominated destination keyring
so that it fails with EDQUOT.

The bug can be triggered using option (3) above using something like the

echo 80 >/proc/sys/kernel/keys/root_maxbytes
keyctl request2 user debug:fred negate @t

The above sets the quota to something much lower (80) to make the bug
easier to trigger, but this is dependent on the system. Note also that
the name of the keyring created contains a random number that may be
between 1 and 10 characters in size, so may throw the test off by
changing the amount of quota used.

Assuming the failure occurs, something like the following will be seen:

kfree_debugcheck: out of range ptr 6b6b6b6b6b6b6b68h
------------[ cut here ]------------
kernel BUG at ../mm/slab.c:2821!
RIP: 0010:[<ffffffff811600f9>] kfree_debugcheck+0x20/0x25
RSP: 0018:ffff8804014a7de8 EFLAGS: 00010092
RAX: 0000000000000034 RBX: 6b6b6b6b6b6b6b68 RCX: 0000000000000000
RDX: 0000000000040001 RSI: 00000000000000f6 RDI: 0000000000000300
RBP: ffff8804014a7df0 R08: 0000000000000001 R09: 0000000000000000
R10: ffff8804014a7e68 R11: 0000000000000054 R12: 0000000000000202
R13: ffffffff81318a66 R14: 0000000000000000 R15: 0000000000000001
Call Trace:

Fixes: f70e2e06196a ('KEYS: Do preallocation for __key_link()')
Signed-off-by: Dan Carpenter <>
Signed-off-by: David Howells <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Jiri Slaby <>
security/keys/key.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/keys/key.c b/security/keys/key.c
index 8fb7c7bd4657..6595b2dd89fe 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -580,7 +580,7 @@ int key_reject_and_link(struct key *key,


- if (keyring)
+ if (keyring && link_ret == 0)
__key_link_end(keyring, key->type, prealloc);

/* wake up anyone waiting for a key to be constructed */
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