[PATCH 6.1] fscrypt: use the mount idmap for the owner check in fscrypt_ioctl_set_policy()

From: Zhan Xusheng <[email protected]>

commit cf6c993c0feca7984797e634deba3c80342e199a upstream.

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: 14f3db5542e6 ("ext4: support idmapped mounts")
Cc: [email protected]
Signed-off-by: Zhan Xusheng <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Eric Biggers <[email protected]>
---
 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 46757c3052ef9..d0f97caa20211 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -494,7 +494,7 @@ int fscrypt_ioctl_set_policy(struct file *filp, const void __user *arg)
 		return -EFAULT;
 	policy.version = version;
 
-	if (!inode_owner_or_capable(&init_user_ns, inode))
+	if (!inode_owner_or_capable(file_mnt_user_ns(filp), inode))
 		return -EACCES;
 
 	ret = mnt_want_write_file(filp);

base-commit: e4f7d8be268ecf717f94ee2e242afa79ddeacaed
-- 
2.55.0