From: Eric Dumazet Date: Thu, 27 Apr 2017 00:15:40 +0000 (-0700) Subject: tcp: do not underestimate skb->truesize in tcp_trim_head() X-Git-Tag: release-20171130_firefly~4^2~100^2~1^2~9^2~12 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=9150b1040111d3b4ff58e19e298da838064ceaac;p=firefly-linux-kernel-4.4.55.git tcp: do not underestimate skb->truesize in tcp_trim_head() [ Upstream commit 7162fb242cb8322beb558828fd26b33c3e9fc805 ] Andrey found a way to trigger the WARN_ON_ONCE(delta < len) in skb_try_coalesce() using syzkaller and a filter attached to a TCP socket over loopback interface. I believe one issue with looped skbs is that tcp_trim_head() can end up producing skb with under estimated truesize. It hardly matters for normal conditions, since packets sent over loopback are never truncated. Bytes trimmed from skb->head should not change skb truesize, since skb->head is not reallocated. Signed-off-by: Eric Dumazet Reported-by: Andrey Konovalov Tested-by: Andrey Konovalov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index de95714d021c..3fdcdc730f71 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1221,7 +1221,7 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len, * eventually). The difference is that pulled data not copied, but * immediately discarded. */ -static void __pskb_trim_head(struct sk_buff *skb, int len) +static int __pskb_trim_head(struct sk_buff *skb, int len) { struct skb_shared_info *shinfo; int i, k, eat; @@ -1231,7 +1231,7 @@ static void __pskb_trim_head(struct sk_buff *skb, int len) __skb_pull(skb, eat); len -= eat; if (!len) - return; + return 0; } eat = len; k = 0; @@ -1257,23 +1257,28 @@ static void __pskb_trim_head(struct sk_buff *skb, int len) skb_reset_tail_pointer(skb); skb->data_len -= len; skb->len = skb->data_len; + return len; } /* Remove acked data from a packet in the transmit queue. */ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len) { + u32 delta_truesize; + if (skb_unclone(skb, GFP_ATOMIC)) return -ENOMEM; - __pskb_trim_head(skb, len); + delta_truesize = __pskb_trim_head(skb, len); TCP_SKB_CB(skb)->seq += len; skb->ip_summed = CHECKSUM_PARTIAL; - skb->truesize -= len; - sk->sk_wmem_queued -= len; - sk_mem_uncharge(sk, len); - sock_set_flag(sk, SOCK_QUEUE_SHRUNK); + if (delta_truesize) { + skb->truesize -= delta_truesize; + sk->sk_wmem_queued -= delta_truesize; + sk_mem_uncharge(sk, delta_truesize); + sock_set_flag(sk, SOCK_QUEUE_SHRUNK); + } /* Any change of skb->len requires recalculation of tso factor. */ if (tcp_skb_pcount(skb) > 1)