diff mbox series

net: Fix potential out of bound write in skb_try_coalesce()

Message ID 1596541698-18938-1-git-send-email-linmiaohe@huawei.com
State Changes Requested
Delegated to: David Miller
Headers show
Series net: Fix potential out of bound write in skb_try_coalesce() | expand

Commit Message

Miaohe Lin Aug. 4, 2020, 11:48 a.m. UTC 
From: Miaohe Lin <linmiaohe@huawei.com>

The head_frag of skb would occupy one extra skb_frag_t. Take it into
account or out of bound write to skb frags may happen.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 net/core/skbuff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Eric Dumazet Aug. 4, 2020, 2:34 p.m. UTC | #1 
On Tue, Aug 4, 2020 at 4:46 AM linmiaohe <linmiaohe@huawei.com> wrote:
>
> From: Miaohe Lin <linmiaohe@huawei.com>
>
> The head_frag of skb would occupy one extra skb_frag_t. Take it into
> account or out of bound write to skb frags may happen.
>
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Please share a stack trace if this was a real bug spotted in the wild.

I do not believe this patch is correct.

if (A + B >= MAX)   is equivalent to  if (A + B + 1 > MAX)

Note how the other condition (when there is no bytes in skb header) is coded :

if (A + B > MAX) return false;

In anycase, please always provide a Fixes: tag for any bug fix.

Thanks.
diff mbox series

Patch

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8a0c39e4ab0a..b489ba201fac 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -5154,7 +5154,7 @@  bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 		unsigned int offset;
 
 		if (to_shinfo->nr_frags +
-		    from_shinfo->nr_frags >= MAX_SKB_FRAGS)
+		    from_shinfo->nr_frags + 1 >= MAX_SKB_FRAGS)
 			return false;
 
 		if (skb_head_is_locked(from))