From b73919e115af86118d7f18ff5f48c8ab0397efea Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Thu, 7 Jun 2018 13:39:49 -0700 Subject: BACKPORT: socket: close race condition between sock_close() and sockfs_setattr() fchownat() doesn't even hold refcnt of fd until it figures out fd is really needed (otherwise is ignored) and releases it after it resolves the path. This means sock_close() could race with sockfs_setattr(), which leads to a NULL pointer dereference since typically we set sock->sk to NULL in ->release(). As pointed out by Al, this is unique to sockfs. So we can fix this in socket layer by acquiring inode_lock in sock_close() and checking against NULL in sockfs_setattr(). sock_release() is called in many places, only the sock_close() path matters here. And fortunately, this should not affect normal sock_close() as it is only called when the last fd refcnt is gone. It only affects sock_close() with a parallel sockfs_setattr() in progress, which is not common. Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.") Reported-by: shankarapailoor Cc: Tetsuo Handa Cc: Lorenzo Colitti Cc: Al Viro Signed-off-by: Cong Wang Signed-off-by: David S. Miller (cherry picked from commit 6d8c50dcb029872b298eea68cc6209c866fd3e14) (use i_mutex directly instead of inode_lock()) Bug: 125367761 Test: used reproducer from Ied4bbca5c7eb80c201fec6e0aabc95c24acc1b59 Change-Id: Icf0824632734bd9d50dda65f87fc130c21b137ac Signed-off-by: Eric Biggers --- net/socket.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'net') diff --git a/net/socket.c b/net/socket.c index b7f357804..2e6a155e2 100644 --- a/net/socket.c +++ b/net/socket.c @@ -524,7 +524,10 @@ static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr) if (!err && (iattr->ia_valid & ATTR_UID)) { struct socket *sock = SOCKET_I(dentry->d_inode); - sock->sk->sk_uid = iattr->ia_uid; + if (sock->sk) + sock->sk->sk_uid = iattr->ia_uid; + else + err = -ENOENT; } return err; @@ -592,12 +595,16 @@ const struct file_operations bad_sock_fops = { * an inode not a file. */ -void sock_release(struct socket *sock) +static void __sock_release(struct socket *sock, struct inode *inode) { if (sock->ops) { struct module *owner = sock->ops->owner; + if (inode) + mutex_lock(&inode->i_mutex); sock->ops->release(sock); + if (inode) + mutex_unlock(&inode->i_mutex); sock->ops = NULL; module_put(owner); } @@ -615,6 +622,11 @@ void sock_release(struct socket *sock) } sock->file = NULL; } + +void sock_release(struct socket *sock) +{ + __sock_release(sock, NULL); +} EXPORT_SYMBOL(sock_release); void sock_tx_timestamp(struct sock *sk, __u8 *tx_flags) @@ -1199,7 +1211,7 @@ static int sock_close(struct inode *inode, struct file *filp) pr_debug(KERN_INFO "[mtk_net][socekt]socket_close[%lu] \n",inode->i_ino); } #endif - sock_release(SOCKET_I(inode)); + __sock_release(SOCKET_I(inode), inode); return 0; } -- cgit v1.2.3