[PATCH 3.10 135/268] af_unix: move unix_mknod() out of bindlock

Willy Tarreau
2017-06-19T19:21:30Z

From: WANG Cong <xiyou.wangcong@gmail.com>

commit 0fb44559ffd67de8517098b81f675fa0210f13f0 upstream.

Dmitry reported a deadlock scenario:

unix_bind() path:
u->bindlock ==> sb_writer

do_splice() path:
sb_writer ==> pipe->mutex ==> u->bindlock

In the unix_bind() code path, unix_mknod() does not have to
be done with u->bindlock held, since it is a pure fs operation,
so we can just move unix_mknod() out.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
net/unix/af_unix.c | 27 ++++++++++++++++-----------
1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 8f118c7..4b18115 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -977,6 +977,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
unsigned int hash;
struct unix_address *addr;
struct hlist_head *list;
+ struct path path = { NULL, NULL };

err = -EINVAL;
if (sunaddr->sun_family != AF_UNIX)
@@ -992,9 +993,20 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
goto out;
addr_len = err;

+ if (sun_path[0]) {
+ umode_t mode = S_IFSOCK |
+ (SOCK_INODE(sock)->i_mode & ~current_umask());
+ err = unix_mknod(sun_path, mode, &path);
+ if (err) {
+ if (err == -EEXIST)
+ err = -EADDRINUSE;
+ goto out;
+ }
+ }
+
err = mutex_lock_interruptible(&u->readlock);
if (err)
- goto out;
+ goto out_put;

err = -EINVAL;
if (u->addr)
@@ -1011,16 +1023,6 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
atomic_set(&addr->refcnt, 1);

if (sun_path[0]) {
- struct path path;
- umode_t mode = S_IFSOCK |
- (SOCK_INODE(sock)->i_mode & ~current_umask());
- err = unix_mknod(sun_path, mode, &path);
- if (err) {
- if (err == -EEXIST)
- err = -EADDRINUSE;
- unix_release_addr(addr);
- goto out_up;
- }
addr->hash = UNIX_HASH_SIZE;
hash = path.dentry->d_inode->i_ino & (UNIX_HASH_SIZE-1);
spin_lock(&unix_table_lock);
@@ -1047,6 +1049,9 @@ out_unlock:
spin_unlock(&unix_table_lock);
out_up:
mutex_unlock(&u->readlock);
+out_put:
+ if (err)
+ path_put(&path);
out:
return err;
}
--
2.8.0.rc2.1.gbe9624a