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Commit 91717ffc authored by Cong Wang's avatar Cong Wang Committed by Greg Kroah-Hartman
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socket: close race condition between sock_close() and sockfs_setattr() 



[ Upstream commit 6d8c50dc ]

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: 86741ec2 ("net: core: Add a UID field to struct sock.")
Reported-by: default avatarshankarapailoor <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: default avatarCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 39f4ae01

net/socket.c

+15 −3
Original line number Original line Diff line number Diff line
@@ -538,7 +538,10 @@ static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr) 
	if (!err && (iattr->ia_valid & ATTR_UID)) {

	if (!err && (iattr->ia_valid & ATTR_UID)) {

		struct socket *sock = SOCKET_I(d_inode(dentry));

		struct socket *sock = SOCKET_I(d_inode(dentry));





		if (sock->sk)

			sock->sk->sk_uid = iattr->ia_uid;

			sock->sk->sk_uid = iattr->ia_uid;

		else

			err = -ENOENT;

	}

	}





	return err;

	return err;
@@ -588,12 +591,16 @@ EXPORT_SYMBOL(sock_alloc); 
 *	an inode not a file.

 *	an inode not a file.

 */

 */





void sock_release(struct socket *sock)

static void __sock_release(struct socket *sock, struct inode *inode)

{

{

	if (sock->ops) {

	if (sock->ops) {

		struct module *owner = sock->ops->owner;

		struct module *owner = sock->ops->owner;





		if (inode)

			inode_lock(inode);

		sock->ops->release(sock);

		sock->ops->release(sock);

		if (inode)

			inode_unlock(inode);

		sock->ops = NULL;

		sock->ops = NULL;

		module_put(owner);

		module_put(owner);

	}

	}
@@ -608,6 +615,11 @@ void sock_release(struct socket *sock) 
	}

	}

	sock->file = NULL;

	sock->file = NULL;

}

}



void sock_release(struct socket *sock)

{

	__sock_release(sock, NULL);

}

EXPORT_SYMBOL(sock_release);

EXPORT_SYMBOL(sock_release);





void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)

void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
@@ -1122,7 +1134,7 @@ static int sock_mmap(struct file *file, struct vm_area_struct *vma) 




static int sock_close(struct inode *inode, struct file *filp)

static int sock_close(struct inode *inode, struct file *filp)

{

{

	sock_release(SOCKET_I(inode));

	__sock_release(SOCKET_I(inode), inode);

	return 0;

	return 0;

}

}