Looks like this might be causing problems, at least for me on ppc. This
happened during a normal boot, right around first interface config/dhcp
run..
cpu 0x0: Vector: 300 (Data Access) at [c00000000147b820]
pc: c000000000435e5c: .sk_filter_delayed_uncharge+0x1c/0x60
lr: c0000000004360d0: .sk_attach_filter+0x170/0x180
sp: c00000000147baa0
msr: 9000000000009032
dar: 4
dsisr: 40000000
current = 0xc000000004780fa0
paca = 0xc000000000650480
pid = 1295, comm = dhclient3
0:mon> t
[c00000000147bb20] c0000000004360d0 .sk_attach_filter+0x170/0x180
[c00000000147bbd0] c000000000418988 .sock_setsockopt+0x788/0x7f0
[c00000000147bcb0] c000000000438a74 .compat_sys_setsockopt+0x4e4/0x5a0
[c00000000147bd90] c00000000043955c .compat_sys_socketcall+0x25c/0x2b0
[c00000000147be30] c000000000007508 syscall_exit+0x0/0x40
--- Exception: c01 (System Call) at 000000000ff618d8
SP (fffdf040) is in userspace
0:mon>
I.e. null pointer deref at sk_filter_delayed_uncharge+0x1c:
0:mon> di $.sk_filter_delayed_uncharge
c000000000435e40 7c0802a6 mflr r0
c000000000435e44 fbc1fff0 std r30,-16(r1)
c000000000435e48 7c8b2378 mr r11,r4
c000000000435e4c ebc2cdd0 ld r30,-12848(r2)
c000000000435e50 f8010010 std r0,16(r1)
c000000000435e54 f821ff81 stdu r1,-128(r1)
c000000000435e58 380300a4 addi r0,r3,164
c000000000435e5c 81240004 lwz r9,4(r4)
That's the deref of fp:
static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
{
unsigned int size = sk_filter_len(fp);
...
That is called from sk_attach_filter():
...
rcu_read_lock_bh();
old_fp = rcu_dereference(sk->sk_filter);
rcu_assign_pointer(sk->sk_filter, fp);
rcu_read_unlock_bh();
sk_filter_delayed_uncharge(sk, old_fp);
return 0;
...
So, looks like rcu_dereference() returned NULL. I don't know the
filter code at all, but it seems like it might be a valid case?
sk_detach_filter() seems to handle a NULL sk_filter, at least.
So, this needs review by someone who knows the filter, but it fixes the
problem for me:
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
9b013e05e0