From cb79a180f2e7eb51de5a4848652893197637bccb Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Wed, 1 Nov 2017 20:30:49 +0100 Subject: [PATCH] xfrm: defer daddr pointer assignment after spi parsing syzbot reports: BUG: KASAN: use-after-free in __xfrm_state_lookup+0x695/0x6b0 Read of size 4 at addr ffff8801d434e538 by task syzkaller647520/2991 [..] __xfrm_state_lookup+0x695/0x6b0 net/xfrm/xfrm_state.c:833 xfrm_state_lookup+0x8a/0x160 net/xfrm/xfrm_state.c:1592 xfrm_input+0x8e5/0x22f0 net/xfrm/xfrm_input.c:302 The use-after-free is the ipv4 destination address, which points to an skb head area that has been reallocated: pskb_expand_head+0x36b/0x1210 net/core/skbuff.c:1494 __pskb_pull_tail+0x14a/0x17c0 net/core/skbuff.c:1877 pskb_may_pull include/linux/skbuff.h:2102 [inline] xfrm_parse_spi+0x3d3/0x4d0 net/xfrm/xfrm_input.c:170 xfrm_input+0xce2/0x22f0 net/xfrm/xfrm_input.c:291 so the real bug is that xfrm_parse_spi() uses pskb_may_pull, but for now do smaller workaround that makes xfrm_input fetch daddr after spi parsing. Reported-by: syzbot Signed-off-by: Florian Westphal Signed-off-by: Steffen Klassert --- net/xfrm/xfrm_input.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c index 8ac9d32fb79d..1c6051cb7733 100644 --- a/net/xfrm/xfrm_input.c +++ b/net/xfrm/xfrm_input.c @@ -265,8 +265,6 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type) goto lock; } - daddr = (xfrm_address_t *)(skb_network_header(skb) + - XFRM_SPI_SKB_CB(skb)->daddroff); family = XFRM_SPI_SKB_CB(skb)->family; /* if tunnel is present override skb->mark value with tunnel i_key */ @@ -293,6 +291,8 @@ int xfrm_input(struct sk_buff *skb, int nexthdr, __be32 spi, int encap_type) goto drop; } + daddr = (xfrm_address_t *)(skb_network_header(skb) + + XFRM_SPI_SKB_CB(skb)->daddroff); do { if (skb->sp->len == XFRM_MAX_DEPTH) { XFRM_INC_STATS(net, LINUX_MIB_XFRMINBUFFERERROR); -- 2.30.2