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Date: Tue, 1 Apr 2008 20:49:04 +0400
From: Evgeniy Polyakov <johnpol@....mipt.ru>
To: David Miller <davem@...emloft.net>
Cc: axboe@...nel.dk, netdev@...r.kernel.org
Subject: Fix for the fundamental network/block layer race in sendfile().
Hi.
Summary of the previous series with this pompous header:
when sendfile() returns, pages which it sent can still be queued in tcp
stack or hardware, so subsequent write into them will endup in
corrupting data which will be eventually sent. This concerns all
->sendpage() users namely sendfile() and splice().
We can only safely reuse that pages only when ack is received from the
remote side, which will force network stack to release pages.
My simple extension allows to hook into data releasing path and perform
any actions we want. This is achieved by replacing skb->destructor with
own callback registerd by interested user, for example splice/sendfile
code. Splice (pipe info structure) in turn is extended to hold atomic
counter of the pages in flight (without structure size change because of
alignment issues it has right now), so splice code will sleep when full
pipe info (->nrbufs pages) was sent, it will wait until number of pages
in flight hits zero, which is decremented in private splice callback.
Patch was tested with simple send and recv applications, which can be
found at
http://tservice.net.ru/~s0mbre/archive/tmp/sendfile_fix/
One has to run them on different machines, since loopback uses a bit
different scheme (namely page is _never_ copied, so when it is received
by 'remote' side, it still exists on the 'local' side, so modifications
will endup in data corruption).
devfs1# ./recv -a 0.0.0.0 -p 1025 -c 1024
devfs2# ./send -a devfs1 -p 1025 -f /tmp/test -c 1024
In case of failure you will get this:
Connected to devfs1:1025.
/tmp/test/1024 -> devfs1:1025
Data was corrupted: ab.
after short period of time, where above 'ab' is a hex byte writen into
mapped file, which has been sent, immediately after senfile()
returns to userspace.
Data is supposed to be always zero, and applications should run forever.
-c parameter specifies number of bytes to be sent in each run of the
sendfile(). It has to be the same on both machines.
Fix attached, consider for inclusion.
Signed-off-by: Evgeniy Polyakov <johnpol@....mipt.ru>
diff --git a/fs/read_write.c b/fs/read_write.c
index 49a9871..8c94e03 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -16,6 +16,7 @@
#include <linux/syscalls.h>
#include <linux/pagemap.h>
#include <linux/splice.h>
+#include <net/sock.h>
#include "read_write.h"
#include <asm/uaccess.h>
@@ -703,6 +704,8 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
loff_t pos;
ssize_t retval;
int fput_needed_in, fput_needed_out, fl;
+ struct sock *sk;
+ struct socket *sock;
/*
* Get input file, and verify that it is ok..
@@ -762,6 +765,12 @@ static ssize_t do_sendfile(int out_fd, int in_fd, loff_t *ppos,
count = max - pos;
}
+ sock = out_file->private_data;
+ sk = sock->sk;
+
+ sk->sk_user_data = &skb_splice_destructor;
+ sk->sk_flags |= SO_PRIVATE_CALLBACK;
+
fl = 0;
#if 0
/*
diff --git a/fs/splice.c b/fs/splice.c
index 0670c91..1432b13 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -29,6 +29,7 @@
#include <linux/syscalls.h>
#include <linux/uio.h>
#include <linux/security.h>
+#include <net/sock.h>
/*
* Attempt to steal a page from a pipe buffer. This should perhaps go into
@@ -535,6 +536,7 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
if (!ret) {
more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
+ buf->page->lru.next = (void *)pipe;
ret = file->f_op->sendpage(file, buf->page, buf->offset,
sd->len, &pos, more);
}
@@ -629,6 +631,8 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
ret = 0;
do_wakeup = 0;
+ atomic_set(&pipe->god_blessed_us, pipe->nrbufs);
+
for (;;) {
if (pipe->nrbufs) {
struct pipe_buffer *buf = pipe->bufs + pipe->curbuf;
@@ -665,12 +669,18 @@ ssize_t __splice_from_pipe(struct pipe_inode_info *pipe, struct splice_desc *sd,
do_wakeup = 1;
}
- if (!sd->total_len)
+ if (!sd->total_len) {
+ wait_event_interruptible(pipe->wait,
+ !atomic_read(&pipe->god_blessed_us));
break;
+ }
}
if (pipe->nrbufs)
continue;
+
+ wait_event_interruptible(pipe->wait, !atomic_read(&pipe->god_blessed_us));
+
if (!pipe->writers)
break;
if (!pipe->waiting_writers) {
diff --git a/include/asm-x86/socket.h b/include/asm-x86/socket.h
index 80af9c4..a4b047e 100644
--- a/include/asm-x86/socket.h
+++ b/include/asm-x86/socket.h
@@ -54,4 +54,6 @@
#define SO_MARK 36
+#define SO_PRIVATE_CALLBACK 37
+
#endif /* _ASM_SOCKET_H */
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 8e41202..465405a 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -51,6 +51,7 @@ struct pipe_inode_info {
unsigned int waiting_writers;
unsigned int r_counter;
unsigned int w_counter;
+ atomic_t god_blessed_us;
struct fasync_struct *fasync_readers;
struct fasync_struct *fasync_writers;
struct inode *inode;
diff --git a/include/net/sock.h b/include/net/sock.h
index fd98760..ac7bc52 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -862,6 +862,8 @@ extern struct sk_buff *sock_rmalloc(struct sock *sk,
extern void sock_wfree(struct sk_buff *skb);
extern void sock_rfree(struct sk_buff *skb);
+extern void skb_splice_destructor(struct sk_buff *skb);
+
extern int sock_setsockopt(struct socket *sock, int level,
int op, char __user *optval,
int optlen);
@@ -1168,6 +1170,8 @@ static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk)
sock_hold(sk);
skb->sk = sk;
skb->destructor = sock_wfree;
+ if (sk->sk_flags & SO_PRIVATE_CALLBACK)
+ skb->destructor = sk->sk_user_data;
atomic_add(skb->truesize, &sk->sk_wmem_alloc);
}
diff --git a/net/core/sock.c b/net/core/sock.c
index 2654c14..0c10581 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -112,6 +112,7 @@
#include <linux/tcp.h>
#include <linux/init.h>
#include <linux/highmem.h>
+#include <linux/pipe_fs_i.h>
#include <asm/uaccess.h>
#include <asm/system.h>
@@ -1116,6 +1117,24 @@ void sock_wfree(struct sk_buff *skb)
sock_put(sk);
}
+void skb_splice_destructor(struct sk_buff *skb)
+{
+ if (skb_shinfo(skb)->nr_frags) {
+ int i;
+ struct pipe_inode_info *pipe;
+
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ struct page *page = skb_shinfo(skb)->frags[i].page;
+
+ pipe = (struct pipe_inode_info *)page->lru.next;
+ if (atomic_dec_return(&pipe->god_blessed_us) == 0)
+ wake_up(&pipe->wait);
+ }
+ }
+
+ sock_wfree(skb);
+}
+
/*
* Read buffer destructor automatically called from kfree_skb.
*/
@@ -2164,6 +2183,7 @@ EXPORT_SYMBOL(sock_no_socketpair);
EXPORT_SYMBOL(sock_rfree);
EXPORT_SYMBOL(sock_setsockopt);
EXPORT_SYMBOL(sock_wfree);
+EXPORT_SYMBOL(skb_splice_destructor);
EXPORT_SYMBOL(sock_wmalloc);
EXPORT_SYMBOL(sock_i_uid);
EXPORT_SYMBOL(sock_i_ino);
--
Evgeniy Polyakov
--
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