When binding a non-abstract AF_UNIX socket it will gain a representation
in the filesystem. Enable the socket infrastructure to handle idmapped
mounts by passing down the user namespace of the mount the socket will
be created from. If the initial user namespace is passed nothing changes
so non-idmapped mounts will see identical behavior as before.

Link: https://lore.kernel.org/r/20210112220124.837960-25-christian.brauner@ubuntu.com (local)
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <redacted>
---
/* v2 */
unchanged

/* v3 */
unchanged

/* v4 */
unchanged

/* v5 */
unchanged
base-commit: 7c53f6b671f4aba70ff15e1b05148b10d58c2837

/* v6 */
unchanged
base-commit: 19c329f6808995b142b3966301f217c831e7cf31
---
 net/unix/af_unix.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 9a1f3c04402e..5a31307ceb76 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c

@@ -996,8 +996,8 @@ static int unix_mknod(const char *sun_path, umode_t mode, struct path *res)
 	 */
 	err = security_path_mknod(&path, dentry, mode, 0);
 	if (!err) {
-		err = vfs_mknod(&init_user_ns, d_inode(path.dentry), dentry,
-				mode, 0);
+		err = vfs_mknod(mnt_user_ns(path.mnt), d_inode(path.dentry),
+				dentry, mode, 0);
 		if (!err) {
 			res->mnt = mntget(path.mnt);
 			res->dentry = dget(dentry);

-- 
2.30.0