[PATCH 3.16 137/192] scsi: scsi_transport_iscsi: fix the issue that iscsi_if_rx doesn't parse nlmsg properly

Ben Hutchings
2017-10-09T13:16:07Z

From: Xin Long <lucien.xin@gmail.com>

commit c88f0e6b06f4092995688211a631bb436125d77b upstream.

ChunYu found a kernel crash by syzkaller:

[ 651.617875] kasan: CONFIG_KASAN_INLINE enabled
[ 651.618217] kasan: GPF could be caused by NULL-ptr deref or user memory access
[ 651.618731] general protection fault: 0000 [#1] SMP KASAN
[ 651.621543] CPU: 1 PID: 9539 Comm: scsi Not tainted 4.11.0.cov #32
[ 651.621938] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[ 651.622309] task: ffff880117780000 task.stack: ffff8800a3188000
[ 651.622762] RIP: 0010:skb_release_data+0x26c/0x590
[...]
[ 651.627260] Call Trace:
[ 651.629156] skb_release_all+0x4f/0x60
[ 651.629450] consume_skb+0x1a5/0x600
[ 651.630705] netlink_unicast+0x505/0x720
[ 651.632345] netlink_sendmsg+0xab2/0xe70
[ 651.633704] sock_sendmsg+0xcf/0x110
[ 651.633942] ___sys_sendmsg+0x833/0x980
[ 651.637117] __sys_sendmsg+0xf3/0x240
[ 651.638820] SyS_sendmsg+0x32/0x50
[ 651.639048] entry_SYSCALL_64_fastpath+0x1f/0xc2

It's caused by skb_shared_info at the end of sk_buff was overwritten by
ISCSI_KEVENT_IF_ERROR when parsing nlmsg info from skb in iscsi_if_rx.

During the loop if skb->len == nlh->nlmsg_len and both are sizeof(*nlh),
ev = nlmsg_data(nlh) will acutally get skb_shinfo(SKB) instead and set a
new value to skb_shinfo(SKB)->nr_frags by ev->type.

This patch is to fix it by checking nlh->nlmsg_len properly there to
avoid over accessing sk_buff.

Reported-by: ChunYu Wang <chunwang@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/scsi/scsi_transport_iscsi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/scsi/scsi_transport_iscsi.c
+++ b/drivers/scsi/scsi_transport_iscsi.c
@@ -3689,7 +3689,7 @@ iscsi_if_rx(struct sk_buff *skb)
uint32_t group;

nlh = nlmsg_hdr(skb);
- if (nlh->nlmsg_len < sizeof(*nlh) ||
+ if (nlh->nlmsg_len < sizeof(*nlh) + sizeof(*ev) ||
skb->len < nlh->nlmsg_len) {
break;
}