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92 lines
3.5 KiB
Diff
92 lines
3.5 KiB
Diff
From 38327424b40bcebe2de92d07312c89360ac9229a Mon Sep 17 00:00:00 2001
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From: Dan Carpenter <dan.carpenter@oracle.com>
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Date: Thu, 16 Jun 2016 15:48:57 +0100
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Subject: KEYS: potential uninitialized variable
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If __key_link_begin() failed then "edit" would be uninitialized. I've
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added a check to fix that.
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This allows a random user to crash the kernel, though it's quite
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difficult to achieve. There are three ways it can be done as the user
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would have to cause an error to occur in __key_link():
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(1) Cause the kernel to run out of memory. In practice, this is difficult
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to achieve without ENOMEM cropping up elsewhere and aborting the
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attempt.
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(2) Revoke the destination keyring between the keyring ID being looked up
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and it being tested for revocation. In practice, this is difficult to
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time correctly because the KEYCTL_REJECT function can only be used
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from the request-key upcall process. Further, users can only make use
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of what's in /sbin/request-key.conf, though this does including a
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rejection debugging test - which means that the destination keyring
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has to be the caller's session keyring in practice.
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(3) Have just enough key quota available to create a key, a new session
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keyring for the upcall and a link in the session keyring, but not then
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sufficient quota to create a link in the nominated destination keyring
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so that it fails with EDQUOT.
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The bug can be triggered using option (3) above using something like the
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following:
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echo 80 >/proc/sys/kernel/keys/root_maxbytes
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keyctl request2 user debug:fred negate @t
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The above sets the quota to something much lower (80) to make the bug
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easier to trigger, but this is dependent on the system. Note also that
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the name of the keyring created contains a random number that may be
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between 1 and 10 characters in size, so may throw the test off by
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changing the amount of quota used.
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Assuming the failure occurs, something like the following will be seen:
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kfree_debugcheck: out of range ptr 6b6b6b6b6b6b6b68h
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------------[ cut here ]------------
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kernel BUG at ../mm/slab.c:2821!
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...
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RIP: 0010:[<ffffffff811600f9>] kfree_debugcheck+0x20/0x25
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RSP: 0018:ffff8804014a7de8 EFLAGS: 00010092
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RAX: 0000000000000034 RBX: 6b6b6b6b6b6b6b68 RCX: 0000000000000000
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RDX: 0000000000040001 RSI: 00000000000000f6 RDI: 0000000000000300
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RBP: ffff8804014a7df0 R08: 0000000000000001 R09: 0000000000000000
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R10: ffff8804014a7e68 R11: 0000000000000054 R12: 0000000000000202
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R13: ffffffff81318a66 R14: 0000000000000000 R15: 0000000000000001
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...
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Call Trace:
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kfree+0xde/0x1bc
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assoc_array_cancel_edit+0x1f/0x36
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__key_link_end+0x55/0x63
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key_reject_and_link+0x124/0x155
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keyctl_reject_key+0xb6/0xe0
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keyctl_negate_key+0x10/0x12
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SyS_keyctl+0x9f/0xe7
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do_syscall_64+0x63/0x13a
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entry_SYSCALL64_slow_path+0x25/0x25
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Fixes: f70e2e06196a ('KEYS: Do preallocation for __key_link()')
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Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
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Signed-off-by: David Howells <dhowells@redhat.com>
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cc: stable@vger.kernel.org
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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security/keys/key.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/security/keys/key.c b/security/keys/key.c
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index bd5a272..346fbf2 100644
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--- a/security/keys/key.c
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+++ b/security/keys/key.c
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@@ -597,7 +597,7 @@ int key_reject_and_link(struct key *key,
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mutex_unlock(&key_construction_mutex);
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- if (keyring)
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+ if (keyring && link_ret == 0)
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__key_link_end(keyring, &key->index_key, edit);
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/* wake up anyone waiting for a key to be constructed */
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--
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cgit v1.1
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