af_unix: move unix_mknod() out of bindlock

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>

1 files changed, 16 insertions, 11 deletions

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 127656ebe7be..cef79873b09d 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -995,6 +995,7 @@ 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)
@@ -1010,9 +1011,20 @@ 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->bindlock);
         if (err)
-                goto out;
+                goto out_put;
 
         err = -EINVAL;
         if (u->addr)
@@ -1029,16 +1041,6 @@ 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 = d_backing_inode(path.dentry)->i_ino & (UNIX_HASH_SIZE - 1);
                 spin_lock(&unix_table_lock);
@@ -1065,6 +1067,9 @@ out_unlock:
         spin_unlock(&unix_table_lock);
 out_up:
         mutex_unlock(&u->bindlock);
+out_put:
+        if (err)
+                path_put(&path);
 out:
         return err;
 }