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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Tue, 3 Jul 2018 07:48:10 +0200
Message-ID: <CACT4Y+bRTF68Jsv8C3PjtKC82NY5RFiNgndeW+-x6PM1_Eof2Q@mail.gmail.com>
Subject: Re: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname_kernel
To:     Ian Kent <raven@themaw.net>
Cc:     tomas <tomasbortoli@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>, autofs@vger.kernel.org
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On Tue, Jul 3, 2018 at 3:34 AM, Ian Kent <raven@themaw.net> wrote:
> On Mon, 2018-07-02 at 14:15 +0200, Dmitry Vyukov wrote:
>> On Mon, Jul 2, 2018 at 1:55 PM, tomas <tomasbortoli@gmail.com> wrote:
>> > Yes, thanks. Please use my full name, Tomas Bortoli.
>>
>>
>> Please also include:
>>
>> Reported-by: syzbot+60c837b428dc84e83a93@syzkaller.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?

It does not matter. It's a real email address too, so CCing it is
fine. So if git does it automatically (does it?) then just go with it.
If you are doing it manually, then it's not necessary to add it to CC.

syzbot will scrape git log later to discover the tag and mark the bug fixed.

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@themaw.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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