linux-kernel - Re: linux-next boot error: general protection fault in tomoyo_get_local

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 15 May 2020 21:13:57 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Alexey Gladkov <gladkov.alexey@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        syzbot <syzbot+c1af344512918c61362c@...kaller.appspotmail.com>,
        jmorris@...ei.org, linux-kernel@...r.kernel.org,
        linux-next@...r.kernel.org, linux-security-module@...r.kernel.org,
        serge@...lyn.com, sfr@...b.auug.org.au,
        syzkaller-bugs@...glegroups.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: linux-next boot error: general protection fault in
 tomoyo_get_local_path

On Sat, May 16, 2020 at 12:36:28AM +0900, Tetsuo Handa wrote:
> On 2020/05/16 0:18, Tetsuo Handa wrote:
> > This is
> > 
> >         if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
> >                 char *ep;
> >                 const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
> >                 struct pid_namespace *proc_pidns = proc_pid_ns(d_inode(dentry)); // <= here
> > 
> >                 if (*ep == '/' && pid && pid ==
> >                     task_tgid_nr_ns(current, proc_pidns)) {
> > 
> > which was added by commit c59f415a7cb6e1e1 ("Use proc_pid_ns() to get pid_namespace from the proc superblock").
> > 
> > @@ -161,9 +162,10 @@ static char *tomoyo_get_local_path(struct dentry *dentry, char * const buffer,
> >         if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
> >                 char *ep;
> >                 const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
> > +               struct pid_namespace *proc_pidns = proc_pid_ns(d_inode(dentry));
> > 
> >                 if (*ep == '/' && pid && pid ==
> > -                   task_tgid_nr_ns(current, sb->s_fs_info)) {
> > +                   task_tgid_nr_ns(current, proc_pidns)) {
> >                         pos = ep - 5;
> >                         if (pos < buffer)
> >                                 goto out;
> > 
> > Alexey and Eric, any clue?
> > 
> 
> A similar bug (racing inode destruction with open() on proc filesystem) was fixed as
> commit 6f7c41374b62fd80 ("tomoyo: Don't use nifty names on sockets."). Then, it might
> not be safe to replace dentry->d_sb->s_fs_info with dentry->d_inode->i_sb->s_fs_info .

Could you explain why do you want to bother with d_inode() anyway?  Anything that
does dentry->d_inode->i_sb can bloody well use dentry->d_sb.  And that's never
changed over the struct dentry lifetime - ->d_sb is set on allocation and never
modified afterwards.