[PATCH AUTOSEL 5.15] umount: Allow superblock owners to force umount

[PATCH AUTOSEL 5.15] umount: Allow superblock owners to force umount

[Sasha Levin]

From: Trond Myklebust <trond.myklebust@hammerspace.com>

[ Upstream commit e1ff7aa34dec7e650159fd7ca8ec6af7cc428d9f ]

Loosen the permission check on forced umount to allow users holding
CAP_SYS_ADMIN privileges in namespaces that are privileged with respect
to the userns that originally mounted the filesystem.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: https://lore.kernel.org/r/12f212d4ef983714d065a6bb372fbb378753bf4c.1742315194.git.trond.myklebust@hammerspace.com
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/namespace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 22af4b6c737f4..642baef4d9aaa 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1734,6 +1734,7 @@ static void warn_mandlock(void)
 static int can_umount(const struct path *path, int flags)
 {
 	struct mount *mnt = real_mount(path->mnt);
+	struct super_block *sb = path->dentry->d_sb;
 
 	if (!may_mount())
 		return -EPERM;
@@ -1743,7 +1744,7 @@ static int can_umount(const struct path *path, int flags)
 		return -EINVAL;
 	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
 		return -EINVAL;
-	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
+	if (flags & MNT_FORCE && !ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 		return -EPERM;
 	return 0;
 }
-- 
2.39.5