From 8522b496f9d0e76a8b7e0b3a742f98ca6d182571 Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Tue, 23 Oct 2007 03:08:26 -0700 Subject: [PATCH] Fix SKB_WITH_OVERHEAD calculations. patch deea84b0ae3d26b41502ae0a39fe7fe134e703d0 in mainline. [NET]: Fix SKB_WITH_OVERHEAD calculation The calculation in SKB_WITH_OVERHEAD is incorrect in that it can cause an overflow across a page boundary which is what it's meant to prevent. In particular, the header length (X) should not be lumped together with skb_shared_info. The latter needs to be aligned properly while the header has no choice but to sit in front of wherever the payload is. Therefore the correct calculation is to take away the aligned size of skb_shared_info, and then subtract the header length. The resulting quantity L satisfies the following inequality: SKB_DATA_ALIGN(L + X) + sizeof(struct skb_shared_info) <= PAGE_SIZE This is the quantity used by alloc_skb to do the actual allocation. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/skbuff.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index a656cecd373c..ed2c4581a293 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -41,8 +41,7 @@ #define SKB_DATA_ALIGN(X) (((X) + (SMP_CACHE_BYTES - 1)) & \ ~(SMP_CACHE_BYTES - 1)) #define SKB_WITH_OVERHEAD(X) \ - (((X) - sizeof(struct skb_shared_info)) & \ - ~(SMP_CACHE_BYTES - 1)) + ((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))) #define SKB_MAX_ORDER(X, ORDER) \ SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X)) #define SKB_MAX_HEAD(X) (SKB_MAX_ORDER((X), 0)) -- 2.39.5