KEYS: Fix short sprintf buffer in /proc/keys show function
[ Upstream commit
03dab869b7b239c4e013ec82aea22e181e441cfc ]
This fixes CVE-2016-7042.
Fix a short sprintf buffer in proc_keys_show(). If the gcc stack protector
is turned on, this can cause a panic due to stack corruption.
The problem is that xbuf[] is not big enough to hold a 64-bit timeout
rendered as weeks:
(gdb) p 0xffffffffffffffffULL/(60*60*24*7)
$2 =
30500568904943
That's 14 chars plus NUL, not 11 chars plus NUL.
Expand the buffer to 16 chars.
I think the unpatched code apparently works if the stack-protector is not
enabled because on a 32-bit machine the buffer won't be overflowed and on a
64-bit machine there's a 64-bit aligned pointer at one side and an int that
isn't checked again on the other side.
The panic incurred looks something like:
Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in:
ffffffff81352ebe
CPU: 0 PID: 1692 Comm: reproducer Not tainted 4.7.2-201.fc24.x86_64 #1
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
0000000000000086 00000000fbbd2679 ffff8800a044bc00 ffffffff813d941f
ffffffff81a28d58 ffff8800a044bc98 ffff8800a044bc88 ffffffff811b2cb6
ffff880000000010 ffff8800a044bc98 ffff8800a044bc30 00000000fbbd2679
Call Trace:
[<
ffffffff813d941f>] dump_stack+0x63/0x84
[<
ffffffff811b2cb6>] panic+0xde/0x22a
[<
ffffffff81352ebe>] ? proc_keys_show+0x3ce/0x3d0
[<
ffffffff8109f7f9>] __stack_chk_fail+0x19/0x30
[<
ffffffff81352ebe>] proc_keys_show+0x3ce/0x3d0
[<
ffffffff81350410>] ? key_validate+0x50/0x50
[<
ffffffff8134db30>] ? key_default_cmp+0x20/0x20
[<
ffffffff8126b31c>] seq_read+0x2cc/0x390
[<
ffffffff812b6b12>] proc_reg_read+0x42/0x70
[<
ffffffff81244fc7>] __vfs_read+0x37/0x150
[<
ffffffff81357020>] ? security_file_permission+0xa0/0xc0
[<
ffffffff81246156>] vfs_read+0x96/0x130
[<
ffffffff81247635>] SyS_read+0x55/0xc0
[<
ffffffff817eb872>] entry_SYSCALL_64_fastpath+0x1a/0xa4
Reported-by: Ondrej Kozina <okozina@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Ondrej Kozina <okozina@redhat.com>
cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
[mainline backport of commit
abe571f80e33d3df7741d15cd03a8b95a93f659f]
Change-Id: I9785f8f6a9bb18d734b75b9c929be90ca433c5ab
Signed-off-by: Jaechul Lee <jcsing.lee@samsung.com>