4.17-stable review patch. If anyone has any objections, please let me know.
------------------
From: Cong Wang xiyou.wangcong@gmail.com
[ Upstream commit 6d8c50dcb029872b298eea68cc6209c866fd3e14 ]
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 shankarapailoor@gmail.com Cc: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Cc: Lorenzo Colitti lorenzo@google.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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/socket.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
--- a/net/socket.c +++ b/net/socket.c @@ -537,7 +537,10 @@ static int sockfs_setattr(struct dentry if (!err && (iattr->ia_valid & ATTR_UID)) { struct socket *sock = SOCKET_I(d_inode(dentry));
- sock->sk->sk_uid = iattr->ia_uid; + if (sock->sk) + sock->sk->sk_uid = iattr->ia_uid; + else + err = -ENOENT; }
return err; @@ -586,12 +589,16 @@ EXPORT_SYMBOL(sock_alloc); * 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) + inode_lock(inode); sock->ops->release(sock); + if (inode) + inode_unlock(inode); sock->ops = NULL; module_put(owner); } @@ -605,6 +612,11 @@ 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(__u16 tsflags, __u8 *tx_flags) @@ -1146,7 +1158,7 @@ static int sock_mmap(struct file *file,
static int sock_close(struct inode *inode, struct file *filp) { - sock_release(SOCKET_I(inode)); + __sock_release(SOCKET_I(inode), inode); return 0; }