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unix_bind_bsd(): move done_path_create() call after dealing with ->bindlock

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Final preparations for doing unlink on failure past the successful
mknod.  We can't hold ->bindlock over ->mknod() or ->unlink(), since
either might do sb_start_write() (e.g. on overlayfs).  However, we
can do it while holding filesystem and VFS locks - doing
	kern_path_create()
	vfs_mknod()
	grab ->bindlock
	if u->addr had been set
		drop ->bindlock
		done_path_create
		return -EINVAL
	else
		assign the address to socket
		drop ->bindlock
		done_path_create
		return 0
would be deadlock-free.  Here we massage unix_bind_bsd() to that
form.  We are still doing equivalent transformations.

Next commit will *not* be an equivalent transformation - it will
add a call of vfs_unlink() before done_path_create() in "alread bound"
case.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Al Viro 2021-06-19 03:50:31 +00:00 committed by David S. Miller
parent 71e6be6f7d
commit 56c1731b28
1 changed files with 11 additions and 15 deletions
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26
net/unix/af_unix.c
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@ -989,8 +989,8 @@ static int unix_bind_bsd(struct sock *sk, struct unix_address *addr)
struct unix_sock *u = unix_sk(sk);
umode_t mode = S_IFSOCK |
(SOCK_INODE(sk->sk_socket)->i_mode & ~current_umask());
struct path parent, path;
struct user_namespace *ns; // barf...
struct path parent;
struct dentry *dentry;
unsigned int hash;
int err;
@ -1008,36 +1008,32 @@ static int unix_bind_bsd(struct sock *sk, struct unix_address *addr)
* All right, let's create it.
*/
err = security_path_mknod(&parent, dentry, mode, 0);
if (!err) {
if (!err)
err = vfs_mknod(ns, d_inode(parent.dentry), dentry, mode, 0);
if (!err) {
path.mnt = mntget(parent.mnt);
path.dentry = dget(dentry);
}
}
done_path_create(&parent, dentry);
if (err)
if (err) {
done_path_create(&parent, dentry);
return err;
}
err = mutex_lock_interruptible(&u->bindlock);
if (err) {
path_put(&path);
done_path_create(&parent, dentry);
return err;
}
if (u->addr) {
mutex_unlock(&u->bindlock);
path_put(&path);
done_path_create(&parent, dentry);
return -EINVAL;
}
addr->hash = UNIX_HASH_SIZE;
hash = d_backing_inode(path.dentry)->i_ino & (UNIX_HASH_SIZE - 1);
hash = d_backing_inode(dentry)->i_ino & (UNIX_HASH_SIZE - 1);
spin_lock(&unix_table_lock);
u->path = path;
u->path.mnt = mntget(parent.mnt);
u->path.dentry = dget(dentry);
__unix_set_addr(sk, addr, hash);
spin_unlock(&unix_table_lock);
mutex_unlock(&u->bindlock);
done_path_create(&parent, dentry);
return 0;
}