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SubjectRe: [PATCH] ext4 crypto: fix to check feature status before get policy
On Sat, Aug 31, 2019 at 06:32:28PM +0800, Chao Yu wrote:
> Hi,
>
> Is this change not necessary? A month has passed...
>
> Thanks,
>
> On 2019/8/4 17:56, Chao Yu wrote:
> > From: Chao Yu <yuchao0@huawei.com>
> >
> > When getting fscrypto policy via EXT4_IOC_GET_ENCRYPTION_POLICY, if
> > encryption feature is off, it's better to return EOPNOTSUPP instead
> > of ENODATA, so let's add ext4_has_feature_encrypt() to do the check
> > for that.
> >
> > Signed-off-by: Chao Yu <yuchao0@huawei.com>
> > ---
> > fs/ext4/ioctl.c | 6 ++++--
> > 1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> > index 442f7ef873fc..bf87835c1237 100644
> > --- a/fs/ext4/ioctl.c
> > +++ b/fs/ext4/ioctl.c
> > @@ -1112,9 +1112,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> > return -EOPNOTSUPP;
> > #endif
> > }
> > - case EXT4_IOC_GET_ENCRYPTION_POLICY:
> > + case EXT4_IOC_GET_ENCRYPTION_POLICY: {
> > + if (!ext4_has_feature_encrypt(sb))
> > + return -EOPNOTSUPP;
> > return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
> > -
> > + }
> > case EXT4_IOC_FSGETXATTR:
> > {
> > struct fsxattr fa;
> >

Sorry, I was preoccupied with all the other fscrypt changes, and was thinking of
waiting until 5.5 for this to avoid a potential extra merge conflict or a
potentially breaking change. Looking at this again though, the new ioctl
FS_IOC_GET_ENCRYPTION_POLICY_EX *does* do the feature check, which doesn't match
the documentation, which implies the check isn't done. Also, f2fs does the
check in FS_IOC_GET_ENCRYPTION_POLICY, so the filesystems are inconsistent.

So, it makes some sense to apply this now. So I've gone ahead and applied the
following to fscrypt.git#master, edited a bit from your original patch:

From 0642ea2409f3bfa105570e12854b8e2628db6835 Mon Sep 17 00:00:00 2001
From: Chao Yu <yuchao0@huawei.com>
Date: Sun, 4 Aug 2019 17:56:43 +0800
Subject: [PATCH] ext4 crypto: fix to check feature status before get policy

When getting fscrypt policy via EXT4_IOC_GET_ENCRYPTION_POLICY, if
encryption feature is off, it's better to return EOPNOTSUPP instead of
ENODATA, so let's add ext4_has_feature_encrypt() to do the check for
that.

This makes it so that all fscrypt ioctls consistently check for the
encryption feature, and makes ext4 consistent with f2fs in this regard.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
[EB - removed unneeded braces, updated the documentation, and
added more explanation to commit message]
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
Documentation/filesystems/fscrypt.rst | 3 ++-
fs/ext4/ioctl.c | 2 ++
2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
index 4289c29d7c5a..8a0700af9596 100644
--- a/Documentation/filesystems/fscrypt.rst
+++ b/Documentation/filesystems/fscrypt.rst
@@ -562,7 +562,8 @@ FS_IOC_GET_ENCRYPTION_POLICY_EX can fail with the following errors:
or this kernel is too old to support FS_IOC_GET_ENCRYPTION_POLICY_EX
(try FS_IOC_GET_ENCRYPTION_POLICY instead)
- ``EOPNOTSUPP``: the kernel was not configured with encryption
- support for this filesystem
+ support for this filesystem, or the filesystem superblock has not
+ had encryption enabled on it
- ``EOVERFLOW``: the file is encrypted and uses a recognized
encryption policy version, but the policy struct does not fit into
the provided buffer
diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index fe5a4b13f939..5703d607f5af 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -1113,6 +1113,8 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
#endif
}
case EXT4_IOC_GET_ENCRYPTION_POLICY:
+ if (!ext4_has_feature_encrypt(sb))
+ return -EOPNOTSUPP;
return fscrypt_ioctl_get_policy(filp, (void __user *)arg);

case FS_IOC_GET_ENCRYPTION_POLICY_EX:
--
2.23.0
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