[patch 25/48] packet: Avoid lock_sock in mmap handler

Greg KH
2009-02-14T01:38:00Z

[-- Attachment #1: packet-avoid-lock_sock-in-mmap-handler.patch --]
[-- Type: text/plain, Size: 2512 bytes --]

2.6.28-stable review patch. If anyone has any objections, please let us know.

------------------

From: Herbert Xu <herbert@gondor.apana.org.au>

[ Upstream commit 905db44087855e3c1709f538ecdc22fd149cadd8 ]

As the mmap handler gets called under mmap_sem, and we may grab
mmap_sem elsewhere under the socket lock to access user data, we
should avoid grabbing the socket lock in the mmap handler.

Since the only thing we care about in the mmap handler is for
pg_vec* to be invariant, i.e., to exclude packet_set_ring, we
can achieve this by simply using a new mutex.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Martin MOKREJŠ <mmokrejs@ribosome.natur.cuni.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/packet/af_packet.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -77,6 +77,7 @@
#include <linux/poll.h>
#include <linux/module.h>
#include <linux/init.h>
+#include <linux/mutex.h>

#ifdef CONFIG_INET
#include <net/inet_common.h>
@@ -175,6 +176,7 @@ struct packet_sock {
#endif
struct packet_type prot_hook;
spinlock_t bind_lock;
+ struct mutex pg_vec_lock;
unsigned int running:1, /* prot_hook is attached*/
auxdata:1,
origdev:1;
@@ -1068,6 +1070,7 @@ static int packet_create(struct net *net
*/

spin_lock_init(&po->bind_lock);
+ mutex_init(&po->pg_vec_lock);
po->prot_hook.func = packet_rcv;

if (sock->type == SOCK_PACKET)
@@ -1863,6 +1866,7 @@ static int packet_set_ring(struct sock *
synchronize_net();

err = -EBUSY;
+ mutex_lock(&po->pg_vec_lock);
if (closing || atomic_read(&po->mapped) == 0) {
err = 0;
#define XC(a, b) ({ __typeof__ ((a)) __t; __t = (a); (a) = (b); __t; })
@@ -1884,6 +1888,7 @@ static int packet_set_ring(struct sock *
if (atomic_read(&po->mapped))
printk(KERN_DEBUG "packet_mmap: vma is busy: %d\n", atomic_read(&po->mapped));
}
+ mutex_unlock(&po->pg_vec_lock);

spin_lock(&po->bind_lock);
if (was_running && !po->running) {
@@ -1916,7 +1921,7 @@ static int packet_mmap(struct file *file

size = vma->vm_end - vma->vm_start;

- lock_sock(sk);
+ mutex_lock(&po->pg_vec_lock);
if (po->pg_vec == NULL)
goto out;
if (size != po->pg_vec_len*po->pg_vec_pages*PAGE_SIZE)
@@ -1939,7 +1944,7 @@ static int packet_mmap(struct file *file
err = 0;

out:
- release_sock(sk);
+ mutex_unlock(&po->pg_vec_lock);
return err;
}
#endif