[ 13/98] tcp: fix skb_availroom()

Greg Kroah-Hartman
2013-03-26T22:43:46Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 16fad69cfe4adbbfa813de516757b87bcae36d93 ]

Chrome OS team reported a crash on a Pixel ChromeBook in TCP stack :

https://code.google.com/p/chromium/issues/detail?id=182056

commit a21d45726acac (tcp: avoid order-1 allocations on wifi and tx
path) did a poor choice adding an 'avail_size' field to skb, while
what we really needed was a 'reserved_tailroom' one.

It would have avoided commit 22b4a4f22da (tcp: fix retransmit of
partially acked frames) and this commit.

Crash occurs because skb_split() is not aware of the 'avail_size'
management (and should not be aware)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Mukesh Agrawal <quiche@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/skbuff.h | 7 +++++--
net/ipv4/tcp.c | 2 +-
net/ipv4/tcp_output.c | 1 -
3 files changed, 6 insertions(+), 4 deletions(-)

--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -491,7 +491,7 @@ struct sk_buff {
union {
__u32 mark;
__u32 dropcount;
- __u32 avail_size;
+ __u32 reserved_tailroom;
};

sk_buff_data_t inner_transport_header;
@@ -1428,7 +1428,10 @@ static inline int skb_tailroom(const str
*/
static inline int skb_availroom(const struct sk_buff *skb)
{
- return skb_is_nonlinear(skb) ? 0 : skb->avail_size - skb->len;
+ if (skb_is_nonlinear(skb))
+ return 0;
+
+ return skb->end - skb->tail - skb->reserved_tailroom;
}

/**
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -773,7 +773,7 @@ struct sk_buff *sk_stream_alloc_skb(stru
* Make sure that we have exactly size bytes
* available to the caller, no more, no less.
*/
- skb->avail_size = size;
+ skb->reserved_tailroom = skb->end - skb->tail - size;
return skb;
}
__kfree_skb(skb);
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1298,7 +1298,6 @@ static void __pskb_trim_head(struct sk_b
eat = min_t(int, len, skb_headlen(skb));
if (eat) {
__skb_pull(skb, eat);
- skb->avail_size -= eat;
len -= eat;
if (!len)
return;