kmemcheck reported this:
kmemcheck: Caught 16-bit read from uninitialized memory (f6c1ba30)
0500110001508abf050010000500000002017300140000006f72672e66726565
i i i i i i i i i i i i i u u u u u u u u u u u u u u u u u u u
^
Pid: 3462, comm: wpa_supplicant Not tainted (2.6.27-rc3-00054-g6397ab9-dirty #13)
EIP: 0060:[<c05de64a>] EFLAGS: 00010296 CPU: 0
EIP is at nla_parse+0x5a/0xf0
EAX: 00000008 EBX: fffffffd ECX: c06f16c0 EDX: 00000005
ESI: 00000010 EDI: f6c1ba30 EBP: f6367c6c ESP: c0a11e88
DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
CR0: 8005003b CR2: f781cc84 CR3: 3632f000 CR4: 000006d0
DR0: c0ead9bc DR1: 00000000 DR2: 00000000 DR3: 00000000
DR6: ffff4ff0 DR7: 00000400
[<c05d4b23>] rtnl_setlink+0x63/0x130
[<c05d5f75>] rtnetlink_rcv_msg+0x165/0x200
[<c05ddf66>] netlink_rcv_skb+0x76/0xa0
[<c05d5dfe>] rtnetlink_rcv+0x1e/0x30
[<c05dda21>] netlink_unicast+0x281/0x290
[<c05ddbe9>] netlink_sendmsg+0x1b9/0x2b0
[<c05beef2>] sock_sendmsg+0xd2/0x100
[<c05bf945>] sys_sendto+0xa5/0xd0
[<c05bf9a6>] sys_send+0x36/0x40
[<c05c03d6>] sys_socketcall+0x1e6/0x2c0
[<c020353b>] sysenter_do_call+0x12/0x3f
[<ffffffff>] 0xffffffff
This is the line in nla_ok():
/**
* nla_ok - check if the netlink attribute fits into the remaining bytes
* @nla: netlink attribute
* @remaining: number of bytes remaining in attribute stream
*/
static inline int nla_ok(const struct nlattr *nla, int remaining)
{
return remaining >= sizeof(*nla) &&
nla->nla_len >= sizeof(*nla) &&
nla->nla_len <= remaining;
}
It turns out that remaining can become negative due to alignment in
nla_next(). But GCC promotes "remaining" to unsigned in the test
against sizeof(*nla) above. Therefore the test succeeds, and the
nla_for_each_attr() may access memory outside the received buffer.
A short example illustrating this point is here:
#include <stdio.h>
main(void)
{
printf("%d\n", -1 >= sizeof(int));
}
...which prints "1".
This patch adds a cast in front of the sizeof so that GCC will make
a signed comparison and fix the illegal memory dereference. With the
patch applied, there is no kmemcheck report.
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
1045b03e07