Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in ovl_path_open()

Sasha Levin
2020-06-23T17:16:17Z

On Tue, Jun 23, 2020 at 08:55:38PM +0530, Naresh Kamboju wrote:
>On Thu, 18 Jun 2020 at 07:18, Sasha Levin <sashal@kernel.org> wrote:
>>
>> From: Miklos Szeredi <mszeredi@redhat.com>
>>
>> [ Upstream commit 56230d956739b9cb1cbde439d76227d77979a04d ]
>>
>> Check permission before opening a real file.
>>
>> ovl_path_open() is used by readdir and copy-up routines.
>>
>> ovl_permission() theoretically already checked copy up permissions, but it
>> doesn't hurt to re-do these checks during the actual copy-up.
>>
>> For directory reading ovl_permission() only checks access to topmost
>> underlying layer. Readdir on a merged directory accesses layers below the
>> topmost one as well. Permission wasn't checked for these layers.
>>
>> Note: modifying ovl_permission() to perform this check would be far more
>> complex and hence more bug prone. The result is less precise permissions
>> returned in access(2). If this turns out to be an issue, we can revisit
>> this bug.
>>
>> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
>> Signed-off-by: Sasha Levin <sashal@kernel.org>
>> ---
>> fs/overlayfs/util.c | 27 ++++++++++++++++++++++++++-
>> 1 file changed, 26 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
>> index afdc2533ce74..76d6610767f6 100644
>> --- a/fs/overlayfs/util.c
>> +++ b/fs/overlayfs/util.c
>> @@ -307,7 +307,32 @@ bool ovl_is_whiteout(struct dentry *dentry)
>>
>> struct file *ovl_path_open(struct path *path, int flags)
>> {
>> - return dentry_open(path, flags | O_NOATIME, current_cred());
>> + struct inode *inode = d_inode(path->dentry);
>> + int err, acc_mode;
>> +
>> + if (flags & ~(O_ACCMODE | O_LARGEFILE))
>> + BUG();
>> +
>> + switch (flags & O_ACCMODE) {
>> + case O_RDONLY:
>> + acc_mode = MAY_READ;
>> + break;
>> + case O_WRONLY:
>> + acc_mode = MAY_WRITE;
>> + break;
>> + default:
>> + BUG();
>
>This BUG: triggered on stable-rc 5.7, 5.4, 4.19 and 4.14.
>
>steps to reproduce:
> - cd /opt/ltp
> - ./runltp -s execveat03

Yup, that patch has been dropped, thanks for testing!

--
Thanks,
Sasha