Patchwork net: gro: fix possible panic in skb_gro_receive()

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Submitter Eric Dumazet
Date Dec. 6, 2012, 11:54 p.m.
Message ID <1354838099.10983.10.camel@edumazet-glaptop>
Download mbox | patch
Permalink /patch/204348/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - Dec. 6, 2012, 11:54 p.m.
From: Eric Dumazet <edumazet@google.com>

commit 2e71a6f8084e (net: gro: selective flush of packets) added
a bug for skbs using frag_list. This part of the GRO stack is rarely
used, as it needs skb not using a page fragment for their skb->head.

Most drivers do use a page fragment, but some of them use GFP_KERNEL
allocations for the initial fill of their RX ring buffer.

napi_gro_flush() overwrite skb->prev that was used for these skb to
point to the last skb in frag_list.

Fix this using a separate field in struct napi_gro_cb to point to the
last fragment.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/netdevice.h |    3 +++
 net/core/dev.c            |    2 ++
 net/core/skbuff.c         |    6 +++---
 3 files changed, 8 insertions(+), 3 deletions(-)



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David Miller - Dec. 7, 2012, 7:41 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 06 Dec 2012 15:54:59 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> commit 2e71a6f8084e (net: gro: selective flush of packets) added
> a bug for skbs using frag_list. This part of the GRO stack is rarely
> used, as it needs skb not using a page fragment for their skb->head.
> 
> Most drivers do use a page fragment, but some of them use GFP_KERNEL
> allocations for the initial fill of their RX ring buffer.
> 
> napi_gro_flush() overwrite skb->prev that was used for these skb to
> point to the last skb in frag_list.
> 
> Fix this using a separate field in struct napi_gro_cb to point to the
> last fragment.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.
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Patch

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f8eda02..a848ffc 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1488,6 +1488,9 @@  struct napi_gro_cb {
 
 	/* Used in ipv6_gro_receive() */
 	int	proto;
+
+	/* used in skb_gro_receive() slow path */
+	struct sk_buff *last;
 };
 
 #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)
diff --git a/net/core/dev.c b/net/core/dev.c
index c0946cb..e5942bf 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3451,6 +3451,8 @@  static int napi_gro_complete(struct sk_buff *skb)
 	struct list_head *head = &ptype_base[ntohs(type) & PTYPE_HASH_MASK];
 	int err = -ENOENT;
 
+	BUILD_BUG_ON(sizeof(struct napi_gro_cb) > sizeof(skb->cb));
+
 	if (NAPI_GRO_CB(skb)->count == 1) {
 		skb_shinfo(skb)->gso_size = 0;
 		goto out;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4007c14..3f0636c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3004,7 +3004,7 @@  int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	skb_shinfo(nskb)->gso_size = pinfo->gso_size;
 	pinfo->gso_size = 0;
 	skb_header_release(p);
-	nskb->prev = p;
+	NAPI_GRO_CB(nskb)->last = p;
 
 	nskb->data_len += p->len;
 	nskb->truesize += p->truesize;
@@ -3030,8 +3030,8 @@  merge:
 
 	__skb_pull(skb, offset);
 
-	p->prev->next = skb;
-	p->prev = skb;
+	NAPI_GRO_CB(p)->last->next = skb;
+	NAPI_GRO_CB(p)->last = skb;
 	skb_header_release(skb);
 
 done: