net: Fix oops when splicing skbs from a frag_list.

Lennert Buytenhek wrote:
> Since 4fb669948116d928ae44262ab7743732c574630d ("net: Optimize memory
> usage when splicing from sockets.") I'm seeing this oops (e.g. in
> 2.6.30-rc3) when splicing from a TCP socket to /dev/null on a driver
> (mv643xx_eth) that uses LRO in the skb mode (lro_receive_skb) rather
> than the frag mode:

My patch incorrectly assumed skb->sk was always valid, but for
"frag_listed" skbs we can only use skb->sk of their parent.

Reported-by: Lennert Buytenhek <buytenh@wantstofly.org>
Debugged-by: Lennert Buytenhek <buytenh@wantstofly.org>
Tested-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 13 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index ce6356cd9f7..f091a5a845c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1365,9 +1365,8 @@ static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
 
 static inline struct page *linear_to_page(struct page *page, unsigned int *len,
                                           unsigned int *offset,
-                                          struct sk_buff *skb)
+                                          struct sk_buff *skb, struct sock *sk)
 {
-        struct sock *sk = skb->sk;
         struct page *p = sk->sk_sndmsg_page;
         unsigned int off;
 
@@ -1405,13 +1404,14 @@ new_page:
  */
 static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
                                 unsigned int *len, unsigned int offset,
-                                struct sk_buff *skb, int linear)
+                                struct sk_buff *skb, int linear,
+                                struct sock *sk)
 {
         if (unlikely(spd->nr_pages == PIPE_BUFFERS))
                 return 1;
 
         if (linear) {
-                page = linear_to_page(page, len, &offset, skb);
+                page = linear_to_page(page, len, &offset, skb, sk);
                 if (!page)
                         return 1;
         } else
@@ -1442,7 +1442,8 @@ static inline void __segment_seek(struct page **page, unsigned int *poff,
 static inline int __splice_segment(struct page *page, unsigned int poff,
                                    unsigned int plen, unsigned int *off,
                                    unsigned int *len, struct sk_buff *skb,
-                                   struct splice_pipe_desc *spd, int linear)
+                                   struct splice_pipe_desc *spd, int linear,
+                                   struct sock *sk)
 {
         if (!*len)
                 return 1;
@@ -1465,7 +1466,7 @@ static inline int __splice_segment(struct page *page, unsigned int poff,
                 /* the linear region may spread across several pages  */
                 flen = min_t(unsigned int, flen, PAGE_SIZE - poff);
 
-                if (spd_fill_page(spd, page, &flen, poff, skb, linear))
+                if (spd_fill_page(spd, page, &flen, poff, skb, linear, sk))
                         return 1;
 
                 __segment_seek(&page, &poff, &plen, flen);
@@ -1481,8 +1482,8 @@ static inline int __splice_segment(struct page *page, unsigned int poff,
  * pipe is full or if we already spliced the requested length.
  */
 static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
-                      unsigned int *len,
-                      struct splice_pipe_desc *spd)
+                             unsigned int *len, struct splice_pipe_desc *spd,
+                             struct sock *sk)
 {
         int seg;
 
@@ -1492,7 +1493,7 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
         if (__splice_segment(virt_to_page(skb->data),
                              (unsigned long) skb->data & (PAGE_SIZE - 1),
                              skb_headlen(skb),
-                             offset, len, skb, spd, 1))
+                             offset, len, skb, spd, 1, sk))
                 return 1;
 
         /*
@@ -1502,7 +1503,7 @@ static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
                 const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];
 
                 if (__splice_segment(f->page, f->page_offset, f->size,
-                                     offset, len, skb, spd, 0))
+                                     offset, len, skb, spd, 0, sk))
                         return 1;
         }
 
@@ -1528,12 +1529,13 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
                 .ops = &sock_pipe_buf_ops,
                 .spd_release = sock_spd_release,
         };
+        struct sock *sk = skb->sk;
 
         /*
          * __skb_splice_bits() only fails if the output has no room left,
          * so no point in going over the frag_list for the error case.
          */
-        if (__skb_splice_bits(skb, &offset, &tlen, &spd))
+        if (__skb_splice_bits(skb, &offset, &tlen, &spd, sk))
                 goto done;
         else if (!tlen)
                 goto done;
@@ -1545,14 +1547,13 @@ int skb_splice_bits(struct sk_buff *skb, unsigned int offset,
                 struct sk_buff *list = skb_shinfo(skb)->frag_list;
 
                 for (; list && tlen; list = list->next) {
-                        if (__skb_splice_bits(list, &offset, &tlen, &spd))
+                        if (__skb_splice_bits(list, &offset, &tlen, &spd, sk))
                                 break;
                 }
         }
 
 done:
         if (spd.nr_pages) {
-                struct sock *sk = skb->sk;
                 int ret;
 
                 /*