linux-kernel - Re: [PATCH v2] relay: handle alloc_percpu returning NULL in relay

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Message-ID: <20200521152514.GA2868125@eldamar.local>
Date:   Thu, 21 May 2020 17:25:14 +0200
From:   Salvatore Bonaccorso <carnil@...ian.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, ajd@...ux.ibm.com, mpe@...erman.id.au,
        syzbot+1e925b4b836afe85a1c6@...kaller-ppc64.appspotmail.com,
        syzbot+587b2421926808309d21@...kaller-ppc64.appspotmail.com,
        syzbot+58320b7171734bf79d26@...kaller.appspotmail.com,
        syzbot+d6074fb08bdb2e010520@...kaller.appspotmail.com,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v2] relay: handle alloc_percpu returning NULL in
 relay_open

Hi,

On Fri, Dec 20, 2019 at 11:00:56AM -0800, David Rientjes wrote:
> On Thu, 19 Dec 2019, Daniel Axtens wrote:
> 
> > alloc_percpu() may return NULL, which means chan->buf may be set to
> > NULL. In that case, when we do *per_cpu_ptr(chan->buf, ...), we
> > dereference an invalid pointer:
> > 
> > BUG: Unable to handle kernel data access at 0x7dae0000
> > Faulting instruction address: 0xc0000000003f3fec
> > ...
> > NIP [c0000000003f3fec] relay_open+0x29c/0x600
> > LR [c0000000003f3fc0] relay_open+0x270/0x600
> > Call Trace:
> > [c000000054353a70] [c0000000003f3fb4] relay_open+0x264/0x600 (unreliable)
> > [c000000054353b00] [c000000000451764] __blk_trace_setup+0x254/0x600
> > [c000000054353bb0] [c000000000451b78] blk_trace_setup+0x68/0xa0
> > [c000000054353c10] [c0000000010da77c] sg_ioctl+0x7bc/0x2e80
> > [c000000054353cd0] [c000000000758cbc] do_vfs_ioctl+0x13c/0x1300
> > [c000000054353d90] [c000000000759f14] ksys_ioctl+0x94/0x130
> > [c000000054353de0] [c000000000759ff8] sys_ioctl+0x48/0xb0
> > [c000000054353e20] [c00000000000bcd0] system_call+0x5c/0x68
> > 
> > Check if alloc_percpu returns NULL.
> > 
> > This was found by syzkaller both on x86 and powerpc, and the reproducer
> > it found on powerpc is capable of hitting the issue as an unprivileged
> > user.
> > 
> > Fixes: 017c59c042d0 ("relay: Use per CPU constructs for the relay channel buffer pointers")
> > Reported-by: syzbot+1e925b4b836afe85a1c6@...kaller-ppc64.appspotmail.com
> > Reported-by: syzbot+587b2421926808309d21@...kaller-ppc64.appspotmail.com
> > Reported-by: syzbot+58320b7171734bf79d26@...kaller.appspotmail.com
> > Reported-by: syzbot+d6074fb08bdb2e010520@...kaller.appspotmail.com
> > Cc: Akash Goel <akash.goel@...el.com>
> > Cc: Andrew Donnellan <ajd@...ux.ibm.com> # syzkaller-ppc64
> > Reviewed-by: Michael Ellerman <mpe@...erman.id.au>
> > Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>
> > Cc: stable@...r.kernel.org # v4.10+
> > Signed-off-by: Daniel Axtens <dja@...ens.net>
> 
> Acked-by: David Rientjes <rientjes@...gle.com>

It looks this one was never applied (which relates to CVE-2019-19462,
as pointed by Guenter in 20191223163610.GA32267@...ck-us.net).

Whas this lost or are there any issues pending?

Regards,
Salvatore