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KEYS: potential uninitialized variable
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 attempt. (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 following: 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: kfree+0xde/0x1bc assoc_array_cancel_edit+0x1f/0x36 __key_link_end+0x55/0x63 key_reject_and_link+0x124/0x155 keyctl_reject_key+0xb6/0xe0 keyctl_negate_key+0x10/0x12 SyS_keyctl+0x9f/0xe7 do_syscall_64+0x63/0x13a entry_SYSCALL64_slow_path+0x25/0x25 Fixes: f70e2e0 ('KEYS: Do preallocation for __key_link()') Signed-off-by: Dan Carpenter <firstname.lastname@example.org> Signed-off-by: David Howells <email@example.com> cc: firstname.lastname@example.org Signed-off-by: Linus Torvalds <email@example.com>
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