linux-kernel - Re: [PATCH 1/2] ecryptfs: fix uid translation for setxattr on security.capability

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Message-ID: <20210122183141.GB81247@sequoia>
Date:   Fri, 22 Jan 2021 12:31:41 -0600
From:   Tyler Hicks <code@...icks.com>
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     "Eric W . Biederman" <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org, linux-unionfs@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, "Serge E . Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 1/2] ecryptfs: fix uid translation for setxattr on
 security.capability

On 2021-01-19 17:22:03, Miklos Szeredi wrote:
> Prior to commit 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into
> vfs_setxattr()") the translation of nscap->rootid did not take stacked
> filesystems (overlayfs and ecryptfs) into account.
> 
> That patch fixed the overlay case, but made the ecryptfs case worse.

Thanks for sending a fix!

I know that you don't have an eCryptfs setup to test with but I'm at a
loss about how to test this from the userns/fscaps side of things. Do
you have a sequence of unshare/setcap/getcap commands that I can run on
a file inside of an eCryptfs mount to verify that the bug exists after
7c03e2cda4a5 and then again to verify that this patch fixes the bug?

Tyler

> 
> Restore old the behavior for ecryptfs that existed before the overlayfs
> fix.  This does not fix ecryptfs's handling of complex user namespace
> setups, but it does make sure existing setups don't regress.
> 
> Reported-by: Eric W. Biederman <ebiederm@...ssion.com>
> Cc: Tyler Hicks <code@...icks.com>
> Fixes: 7c03e2cda4a5 ("vfs: move cap_convert_nscap() call into vfs_setxattr()")
> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
> ---
>  fs/ecryptfs/inode.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index e23752d9a79f..58d0f7187997 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -1016,15 +1016,19 @@ ecryptfs_setxattr(struct dentry *dentry, struct inode *inode,
>  {
>  	int rc;
>  	struct dentry *lower_dentry;
> +	struct inode *lower_inode;
>  
>  	lower_dentry = ecryptfs_dentry_to_lower(dentry);
> -	if (!(d_inode(lower_dentry)->i_opflags & IOP_XATTR)) {
> +	lower_inode = d_inode(lower_dentry);
> +	if (!(lower_inode->i_opflags & IOP_XATTR)) {
>  		rc = -EOPNOTSUPP;
>  		goto out;
>  	}
> -	rc = vfs_setxattr(lower_dentry, name, value, size, flags);
> +	inode_lock(lower_inode);
> +	rc = __vfs_setxattr_locked(lower_dentry, name, value, size, flags, NULL);
> +	inode_unlock(lower_inode);
>  	if (!rc && inode)
> -		fsstack_copy_attr_all(inode, d_inode(lower_dentry));
> +		fsstack_copy_attr_all(inode, lower_inode);
>  out:
>  	return rc;
>  }
> -- 
> 2.26.2
>