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Commit 158f323b authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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net: adjust skb->truesize in pskb_expand_head() 



Slava Shwartsman reported a warning in skb_try_coalesce(), when we
detect skb->truesize is completely wrong.

In his case, issue came from IPv6 reassembly coping with malicious
datagrams, that forced various pskb_may_pull() to reallocate a bigger
skb->head than the one allocated by NIC driver before entering GRO
layer.

Current code does not change skb->truesize, leaving this burden to
callers if they care enough.

Blindly changing skb->truesize in pskb_expand_head() is not
easy, as some producers might track skb->truesize, for example
in xmit path for back pressure feedback (sk->sk_wmem_alloc)

We can detect the cases where it should be safe to change
skb->truesize :

1) skb is not attached to a socket.
2) If it is attached to a socket, destructor is sock_edemux()

My audit gave only two callers doing their own skb->truesize
manipulation.

I had to remove skb parameter in sock_edemux macro when
CONFIG_INET is not set to avoid a compile error.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarSlava Shwartsman <slavash@mellanox.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b41fd8fd

include/net/sock.h

+1 −1
Original line number Diff line number Diff line
@@ -1534,7 +1534,7 @@ void sock_efree(struct sk_buff *skb); 
#ifdef CONFIG_INET

void sock_edemux(struct sk_buff *skb);

#else

#define sock_edemux(skb) sock_efree(skb)

#define sock_edemux sock_efree

#endif



int sock_setsockopt(struct socket *sock, int level, int op,

net/core/skbuff.c

+11 −3
Original line number Diff line number Diff line
@@ -1192,10 +1192,10 @@ EXPORT_SYMBOL(__pskb_copy_fclone); 
int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,

		     gfp_t gfp_mask)

{

	int i;

	u8 *data;

	int size = nhead + skb_end_offset(skb) + ntail;

	int i, osize = skb_end_offset(skb);

	int size = osize + nhead + ntail;

	long off;

	u8 *data;



	BUG_ON(nhead < 0);
@@ -1257,6 +1257,14 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, 
	skb->hdr_len  = 0;

	skb->nohdr    = 0;

	atomic_set(&skb_shinfo(skb)->dataref, 1);



	/* It is not generally safe to change skb->truesize.

	 * For the moment, we really care of rx path, or

	 * when skb is orphaned (not attached to a socket).

	 */

	if (!skb->sk || skb->destructor == sock_edemux)

		skb->truesize += size - osize;



	return 0;



nofrags:

net/netlink/af_netlink.c

+3 −5
Original line number Diff line number Diff line
@@ -1210,11 +1210,9 @@ static struct sk_buff *netlink_trim(struct sk_buff *skb, gfp_t allocation) 
		skb = nskb;

	}



	if (!pskb_expand_head(skb, 0, -delta,

	pskb_expand_head(skb, 0, -delta,

			 (allocation & ~__GFP_DIRECT_RECLAIM) |

			      __GFP_NOWARN | __GFP_NORETRY))

		skb->truesize -= delta;



			 __GFP_NOWARN | __GFP_NORETRY);

	return skb;

}

net/wireless/util.c

+0 −2
Original line number Diff line number Diff line
@@ -618,8 +618,6 @@ int ieee80211_data_from_8023(struct sk_buff *skb, const u8 *addr, 


		if (pskb_expand_head(skb, head_need, 0, GFP_ATOMIC))

			return -ENOMEM;



		skb->truesize += head_need;

	}



	if (encaps_data) {