[PATCH] fscrypt: use the mount idmap for the owner check in fscrypt_ioctl_set_policy()

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

From: Zhan Xusheng <zhanxusheng@xiaomi.com>

fscrypt_ioctl_set_policy() calls inode_owner_or_capable() with
&nop_mnt_idmap before allowing an encryption policy to be set, instead of
the idmap of the mount the ioctl was issued on.

fscrypt is used by filesystems that support idmapped mounts (e.g. ext4,
f2fs), so on such a mount this compares the caller's fsuid against the
unmapped on-disk owner rather than the mapped owner: the actual owner can
be wrongly denied with -EACCES and an unrelated caller wrongly allowed.
Use file_mnt_idmap(filp) instead.

Fixes: 01beba7957a2 ("fs: port inode_owner_or_capable() to mnt_idmap")
Cc: stable@vger.kernel.org
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
---
 fs/crypto/policy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 9915e39362db..c80b24a941ad 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -534,7 +534,7 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
 		return -EFAULT;
 	policy.version = version;
 
-	if (!inode_owner_or_capable(&nop_mnt_idmap, inode))
+	if (!inode_owner_or_capable(file_mnt_idmap(filp), inode))
 		return -EACCES;
 
 	ret = mnt_want_write_file(filp);
-- 
2.43.0