linux-kernel - [PATCH 3.2 64/74] scsi: scsi_transport_iscsi: fix the issue that iscsi_if

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Message-ID: <lsq.1507552234.401760506@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:30:34 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Chris Leech" <cleech@...hat.com>,
        "Xin Long" <lucien.xin@...il.com>,
        "ChunYu Wang" <chunwang@...hat.com>
Subject: [PATCH 3.2 64/74] scsi: scsi_transport_iscsi: fix the issue that
 iscsi_if_rx doesn't parse nlmsg properly

3.2.94-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@...il.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@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
Acked-by: Chris Leech <cleech@...hat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.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
@@ -2079,7 +2079,7 @@ 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;
 		}