linux-kernel - Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in ovl_path

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Date:   Tue, 23 Jun 2020 13:16:13 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        linux- stable <stable@...r.kernel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        linux-unionfs@...r.kernel.org, lkft-triage@...ts.linaro.org
Subject: Re: [PATCH AUTOSEL 4.14 090/108] ovl: verify permissions in
 ovl_path_open()

On Tue, Jun 23, 2020 at 08:55:38PM +0530, Naresh Kamboju wrote:
>On Thu, 18 Jun 2020 at 07:18, Sasha Levin <sashal@...nel.org> wrote:
>>
>> From: Miklos Szeredi <mszeredi@...hat.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@...hat.com>
>> Signed-off-by: Sasha Levin <sashal@...nel.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