[PATCH] fscrypto: add authorization check for setting encryption policy

[PATCH] fscrypto: add authorization check for setting encryption policy

[Eric Biggers]

On an ext4 or f2fs filesystem with file encryption supported, a user
could set an encryption policy on any empty directory(*) to which they
had readonly access.  This is obviously problematic, since such a
directory might be owned by another user and the new encryption policy
would prevent that other user from creating files in their own directory
(for example).

Fix this by requiring inode_owner_or_capable() permission to set an
encryption policy.  This means that either the caller must own the file,
or the caller must have the capability CAP_FOWNER.

(*) Or also on any regular file, for f2fs v4.6 and later and ext4
    v4.8-rc1 and later; a separate bug fix is coming for that.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
---
 fs/crypto/policy.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 0f9961e..c9800b1 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -95,6 +95,9 @@ static int create_encryption_context_from_policy(struct inode *inode,
 int fscrypt_process_policy(struct inode *inode,
 				const struct fscrypt_policy *policy)
 {
+	if (!inode_owner_or_capable(inode))
+		return -EACCES;
+
 	if (policy->version != 0)
 		return -EINVAL;
 
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH] fscrypto: add authorization check for setting encryption policy

[Eric Biggers]

(Fixing Cc list: the F2FS mailing list is
linux-f2fs-devel@lists.sourceforge.net, not linux-f2fs@vger.kernel.org.)

On Thu, Sep 08, 2016 at 10:57:08AM -0700, Eric Biggers wrote:
> On an ext4 or f2fs filesystem with file encryption supported, a user
> could set an encryption policy on any empty directory(*) to which they
> had readonly access.  This is obviously problematic, since such a
> directory might be owned by another user and the new encryption policy
> would prevent that other user from creating files in their own directory
> (for example).
> 
> Fix this by requiring inode_owner_or_capable() permission to set an
> encryption policy.  This means that either the caller must own the file,
> or the caller must have the capability CAP_FOWNER.
> 
> (*) Or also on any regular file, for f2fs v4.6 and later and ext4
>     v4.8-rc1 and later; a separate bug fix is coming for that.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
> ---
>  fs/crypto/policy.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
> index 0f9961e..c9800b1 100644
> --- a/fs/crypto/policy.c
> +++ b/fs/crypto/policy.c
> @@ -95,6 +95,9 @@ static int create_encryption_context_from_policy(struct inode *inode,
>  int fscrypt_process_policy(struct inode *inode,
>  				const struct fscrypt_policy *policy)
>  {
> +	if (!inode_owner_or_capable(inode))
> +		return -EACCES;
> +
>  	if (policy->version != 0)
>  		return -EINVAL;
>  
> -- 
> 2.8.0.rc3.226.g39d4020
> 

Re: [PATCH] fscrypto: add authorization check for setting encryption policy

[Theodore Ts'o]

On Thu, Sep 08, 2016 at 10:57:08AM -0700, Eric Biggers wrote:
> On an ext4 or f2fs filesystem with file encryption supported, a user
> could set an encryption policy on any empty directory(*) to which they
> had readonly access.  This is obviously problematic, since such a
> directory might be owned by another user and the new encryption policy
> would prevent that other user from creating files in their own directory
> (for example).
> 
> Fix this by requiring inode_owner_or_capable() permission to set an
> encryption policy.  This means that either the caller must own the file,
> or the caller must have the capability CAP_FOWNER.
> 
> (*) Or also on any regular file, for f2fs v4.6 and later and ext4
>     v4.8-rc1 and later; a separate bug fix is coming for that.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}

Thanks, applied.  (Jaeguk, I plan to send this to Linus via the
ext4.git tree as a fix for v4.8)

					- Ted

Re: [PATCH] fscrypto: add authorization check for setting encryption policy

[Jaegeuk Kim]

On Fri, Sep 09, 2016 at 11:37:59PM -0400, Theodore Ts'o wrote:
> On Thu, Sep 08, 2016 at 10:57:08AM -0700, Eric Biggers wrote:
> > On an ext4 or f2fs filesystem with file encryption supported, a user
> > could set an encryption policy on any empty directory(*) to which they
> > had readonly access.  This is obviously problematic, since such a
> > directory might be owned by another user and the new encryption policy
> > would prevent that other user from creating files in their own directory
> > (for example).
> > 
> > Fix this by requiring inode_owner_or_capable() permission to set an
> > encryption policy.  This means that either the caller must own the file,
> > or the caller must have the capability CAP_FOWNER.
> > 
> > (*) Or also on any regular file, for f2fs v4.6 and later and ext4
> >     v4.8-rc1 and later; a separate bug fix is coming for that.
> > 
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
> 
> Thanks, applied.  (Jaeguk, I plan to send this to Linus via the
> ext4.git tree as a fix for v4.8)

Sure, no problem.

> 
> 					- Ted