linux-kernel - Re: [PATCH for v4.9 LTS 72/87] libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount

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Date:   Sat, 15 Jul 2017 15:46:20 +0000
From:   "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH for v4.9 LTS 72/87] libfs: Modify mount_pseudo_xattr to be
 clear it is not a userspace mount

On Sat, Jul 15, 2017 at 02:50:30AM -0500, Eric W. Biederman wrote:
>
>*Scratches my head*
>
>Is there code in v4.9 where this matters?  At the time I merged this to
>my knowledge there were no in kernel users that cared.  Which is why I
>did not cc stable in the first place.

Hey Eric,

We're trying to go over older commits and figure out if they should have been in -stable even though they're not marked for stable.

Because of cases like these, they get to be reviewed a bunch more to verify that indeed should go into -stable, which is why you got this mail.

I'll drop this patch from the queue.

>
>Eric
>
>
>"Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com> writes:
>
>> From: "Eric W. Biederman" <ebiederm@...ssion.com>
>>
>> [ Upstream commit 75422726b0f717d67db3283c2eb5bc14fa2619c5 ]
>>
>> Add MS_KERNMOUNT to the flags that are passed.
>> Use sget_userns and force &init_user_ns instead of calling sget so that
>> even if called from a weird context the internal filesystem will be
>> considered to be in the intial user namespace.
>>
>> Luis Ressel reported that the the failure to pass MS_KERNMOUNT into
>> mount_pseudo broke his in development graphics driver that uses the
>> generic drm infrastructure.  I am not certain the deriver was bug
>> free in it's usage of that infrastructure but since
>> mount_pseudo_xattr can never be triggered by userspace it is clearer
>> and less error prone, and less problematic for the code to be explicit.
>>
>> Reported-by: Luis Ressel <aranea@...ah.de>
>> Tested-by: Luis Ressel <aranea@...ah.de>
>> Acked-by: Al Viro <viro@...IV.linux.org.uk>
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
>> ---
>>  fs/libfs.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/libfs.c b/fs/libfs.c
>> index 48826d4da189..9588780ad43e 100644
>> --- a/fs/libfs.c
>> +++ b/fs/libfs.c
>> @@ -245,7 +245,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
>>  	struct inode *root;
>>  	struct qstr d_name = QSTR_INIT(name, strlen(name));
>>
>> -	s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
>> +	s = sget_userns(fs_type, NULL, set_anon_super, MS_KERNMOUNT|MS_NOUSER,
>> +			&init_user_ns, NULL);
>>  	if (IS_ERR(s))
>>  		return ERR_CAST(s);

-- 

Thanks,
Sasha