linux-kernel - Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname

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Date:   Tue, 03 Jul 2018 09:34:03 +0800
From:   Ian Kent <raven@...maw.net>
To:     Dmitry Vyukov <dvyukov@...gle.com>, tomas <tomasbortoli@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>, autofs@...r.kernel.org
Subject: Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in
 getname_kernel

On Mon, 2018-07-02 at 14:15 +0200, Dmitry Vyukov wrote:
> On Mon, Jul 2, 2018 at 1:55 PM, tomas <tomasbortoli@...il.com> wrote:
> > Yes, thanks. Please use my full name, Tomas Bortoli.
> 
> 
> Please also include:
> 
> Reported-by: syzbot+60c837b428dc84e83a93@...kaller.appspotmail.com

Done.

> 
> from the original bug report. This this help to keep automatic testing
> process running.

Umm ... should I include this email address on the actual cc when
submitting the patch?

> 
> Thanks
> 
> 
> > 
> > On 07/02/2018 12:20 PM, Ian Kent wrote:
> > > On Mon, 2018-07-02 at 10:31 +0200, tomas wrote:
> > > > Hi Ian,
> > > > 
> > > > you are welcome!
> > > > 
> > > > yes your patch is much better. You should just put the "_IOC_NR" macro
> > > > around "cmd" in the lines added to "validate_dev_ioctl" to make it work.
> > > 
> > > LOL, yes, that was a dumb mistake.
> > > 
> > > I'll send it to Andrew Morton, after some fairly simple sanity testing,
> > > with both our Signed-off-by added.
> > > 
> > > > Tomas
> > > > 
> > > > 
> > > > On 07/02/2018 03:42 AM, Ian Kent wrote:
> > > > > On Mon, 2018-07-02 at 09:10 +0800, Ian Kent wrote:
> > > > > > On Mon, 2018-07-02 at 00:04 +0200, tomas wrote:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > I've looked into this issue found by Syzbot and I made a patch:
> > > > > > > 
> > > > > > > https://syzkaller.appspot.com/bug?id=d03abd8b42847f7f69b1d1d7f9720
> > > > > > > 8ae425
> > > > > > > b116
> > > > > > > 3
> > > > > > 
> > > > > > Umm ... oops!
> > > > > > 
> > > > > > Thanks for looking into this Tomas.
> > > > > > 
> > > > > > > The autofs subsystem does not check that the "path" parameter is
> > > > > > > present
> > > > > > > within the "param" struct passed by the userspace in case the
> > > > > > > AUTOFS_DEV_IOCTL_OPENMOUNT_CMD command is passed. Indeed, it
> > > > > > > assumes a
> > > > > > > path is always provided (though a path is not always present, as
> > > > > > > per how
> > > > > > > the struct is defined:
> > > > > > > https://github.com/torvalds/linux/blob/master/include/uapi/linux/a
> > > > > > > uto_de
> > > > > > > v-io
> > > > > > > ct
> > > > > > > l.h#L89).
> > > > > > > Skipping the check provokes an oob read in "strlen", called by
> > > > > > > "getname_kernel", in turn called by the autofs to assess the
> > > > > > > length of
> > > > > > > the non-existing path.
> > > > > > > 
> > > > > > > To solve it, modify the "validate_dev_ioctl" function to check
> > > > > > > also that
> > > > > > > a path has been provided if the command is
> > > > > > > AUTOFS_DEV_IOCTL_OPENMOUNT_CMD.
> > > > > > > 
> > > > > > > 
> > > > > > > --- b/fs/autofs/dev-ioctl.c    2018-07-01 23:10:16.059728621
> > > > > > > +0200around
> > > > > > > +++ a/fs/autofs/dev-ioctl.c    2018-07-01 23:10:24.311792133 +0200
> > > > > > > @@ -136,6 +136,9 @@ static int validate_dev_ioctl(int cmd, s
> > > > > > >              goto out;
> > > > > > >          }
> > > > > > >      }
> > > > > > > +    /* AUTOFS_DEV_IOCTL_OPENMOUNT_CMD without path */
> > > > > > > +    else if(_IOC_NR(cmd) == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD)
> > > > > > > +        return -EINVAL;
> > > > > > 
> > > > > > My preference is to put the comment inside the else but ...
> > > > > > 
> > > > > > There's another question, should the check be done in
> > > > > > autofs_dev_ioctl_openmount() in the same way it's checked in other
> > > > > > ioctls that need a path, such as in autofs_dev_ioctl_requester()
> > > > > > and autofs_dev_ioctl_ismountpoint()?
> > > > > > 
> > > > > > For consistency I'd say it should.
> > > > > > 
> > > > > > > 
> > > > > > >      err = 0;You should just put the "_IOC_NR" directive around
> > > > > > > "cmd" in
> > > > > > > the lines added to "validate_dev_ioctl" to make it work.
> > > > > > >  out:
> > > > > > > 
> > > > > > > 
> > > > > > > Tested and solves the issue on Linus' main git tree.
> > > > > > > 
> > > > > > > 
> > > > > 
> > > > > Or perhaps this (not even compile tested) patch would be better?
> > > > > 
> > > > > autofs - fix slab out of bounds read in getname_kernel()
> > > > > 
> > > > > From: Ian Kent <raven@...maw.net>
> > > > > 
> > > > > The autofs subsystem does not check that the "path" parameter is
> > > > > present for all cases where it is required when it is passed in
> > > > > via the "param" struct.
> > > > > 
> > > > > In particular it isn't checked for the AUTOFS_DEV_IOCTL_OPENMOUNT_CMD
> > > > > ioctl command.
> > > > > 
> > > > > To solve it, modify validate_dev_ioctl() function to check that a
> > > > > path has been provided for ioctl commands that require it.
> > > > > ---
> > > > >  fs/autofs/dev-ioctl.c |   15 +++++++--------
> > > > >  1 file changed, 7 insertions(+), 8 deletions(-)
> > > > > 
> > > > > diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
> > > > > index ea4ca1445ab7..61c63715c3fb 100644
> > > > > --- a/fs/autofs/dev-ioctl.c
> > > > > +++ b/fs/autofs/dev-ioctl.c
> > > > > @@ -135,6 +135,11 @@ static int validate_dev_ioctl(int cmd, struct
> > > > > autofs_dev_ioctl *param)
> > > > >                             cmd);
> > > > >                     goto out;
> > > > >             }
> > > > > +   } else if (cmd == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD ||
> > > > > +              cmd == AUTOFS_DEV_IOCTL_REQUESTER_CMD ||
> > > > > +              cmd == AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD) {
> > > > > +           err = -EINVAL;
> > > > > +           goto out;
> > > > >     }
> > > > > 
> > > > >     err = 0;
> > > > > @@ -433,10 +438,7 @@ static int autofs_dev_ioctl_requester(struct file
> > > > > *fp,
> > > > >     dev_t devid;
> > > > >     int err = -ENOENT;
> > > > > 
> > > > > -   if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
> > > > > -           err = -EINVAL;
> > > > > -           goto out;
> > > > > -   }
> > > > > +   /* param->path has already been checked */
> > > > > 
> > > > >     devid = sbi->sb->s_dev;
> > > > > 
> > > > > @@ -521,10 +523,7 @@ static int autofs_dev_ioctl_ismountpoint(struct
> > > > > file
> > > > > *fp,
> > > > >     unsigned int devid, magic;
> > > > >     int err = -ENOENT;
> > > > > 
> > > > > -   if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
> > > > > -           err = -EINVAL;
> > > > > -           goto out;
> > > > > -   }
> > > > > +   /* param->path has already been checked */
> > > > > 
> > > > >     name = param->path;
> > > > >     type = param->ismountpoint.in.type;
> > 
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