[PATCH 5.15] filelocks: use mount idmapping for setlease permission check

["Seth Forshee (DigitalOcean)" <sforshee@kernel.org>]

From: Seth Forshee <sforshee@kernel.org>

[ Upstream commit 42d0c4bdf753063b6eec55415003184d3ca24f6e ]

A user should be allowed to take out a lease via an idmapped mount if
the fsuid matches the mapped uid of the inode. generic_setlease() is
checking the unmapped inode uid, causing these operations to be denied.

Fix this by comparing against the mapped inode uid instead of the
unmapped uid.

Fixes: 9caccd41541a ("fs: introduce MOUNT_ATTR_IDMAP")
Cc: stable@vger.kernel.org
Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
 fs/locks.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/locks.c b/fs/locks.c
index 82a4487e95b3..881fd16905c6 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1901,9 +1901,10 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
 			void **priv)
 {
 	struct inode *inode = locks_inode(filp);
+	kuid_t uid = i_uid_into_mnt(file_mnt_user_ns(filp), inode);
 	int error;
 
-	if ((!uid_eq(current_fsuid(), inode->i_uid)) && !capable(CAP_LEASE))
+	if ((!uid_eq(current_fsuid(), uid)) && !capable(CAP_LEASE))
 		return -EACCES;
 	if (!S_ISREG(inode->i_mode))
 		return -EINVAL;
-- 
2.39.1