From 6d8c50dcb029872b298eea68cc6209c866fd3e14 Mon Sep 17 00:00:00 2001 From: Cong Wang Date: Thu, 7 Jun 2018 13:39:49 -0700 Subject: [PATCH] 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 --- net/socket.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/net/socket.c b/net/socket.c index af57d85bcb48..8a109012608a 100644 --- a/net/socket.c +++ b/net/socket.c @@ -541,7 +541,10 @@ static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr) 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; @@ -590,12 +593,16 @@ 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); } @@ -609,6 +616,11 @@ 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) @@ -1171,7 +1183,7 @@ static int sock_mmap(struct file *file, struct vm_area_struct *vma) static int sock_close(struct inode *inode, struct file *filp) { - sock_release(SOCKET_I(inode)); + __sock_release(SOCKET_I(inode), inode); return 0; } -- 2.17.1