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Date:   Fri, 20 Dec 2019 11:00:56 -0800 (PST)
From:   David Rientjes <rientjes@google.com>
To:     Daniel Axtens <dja@axtens.net>
cc:     linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
        ajd@linux.ibm.com, mpe@ellerman.id.au,
        syzbot+1e925b4b836afe85a1c6@syzkaller-ppc64.appspotmail.com,
        syzbot+587b2421926808309d21@syzkaller-ppc64.appspotmail.com,
        syzbot+58320b7171734bf79d26@syzkaller.appspotmail.com,
        syzbot+d6074fb08bdb2e010520@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] relay: handle alloc_percpu returning NULL in
 relay_open
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References: <20191219121256.26480-1-dja@axtens.net>
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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@syzkaller-ppc64.appspotmail.com
> Reported-by: syzbot+587b2421926808309d21@syzkaller-ppc64.appspotmail.com
> Reported-by: syzbot+58320b7171734bf79d26@syzkaller.appspotmail.com
> Reported-by: syzbot+d6074fb08bdb2e010520@syzkaller.appspotmail.com
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Andrew Donnellan <ajd@linux.ibm.com> # syzkaller-ppc64
> Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
> Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
> Cc: stable@vger.kernel.org # v4.10+
> Signed-off-by: Daniel Axtens <dja@axtens.net>

Acked-by: David Rientjes <rientjes@google.com>