linux-kernel - Re: [RFC/PATCH] revoke/frevoke system calls

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Date:	Sat, 22 Jul 2006 04:05:19 -0400
From:	"Albert Cahalan" <acahalan@...il.com>
To:	froese@....de, B.Steinbrink@....de, hurtta+gmane@...lo.fmi.fi,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC/PATCH] revoke/frevoke system calls

Edgar Toernig writes:
> Bjvrn Steinbrink wrote:

>> In do_revoke() there is:
>>
>> +    if (current->fsuid != inode->i_uid && !capable(CAP_FOWNER)) {
>> +            ret = -EPERM;
>> +            goto out;
>>
>> That pretty much matches what the BSD manpage says.
>
> Urgs, so any user may remove mappings from another process and
> let it crash?

Two good solutions come to mind:

a. substitute the zero page
b. make the mapping private and touch it as if C-O-W happened

Other concerns:

Optionally excluding the current UID/TGID/TID would be good.
(some flags) A revokeat() call seems to be required. Be sure
to handle working directories. The controlling tty is special.
Flag processes with revoked ttys in /proc/*/stat please, so
that ps can report it properly without opening another file.

BTW, it is wonderful to see this happening.
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