Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 23 Dec 2019 08:36:10 -0800 | From | Guenter Roeck <> | Subject | Re: [PATCH] relay: handle alloc_percpu returning NULL in relay_open |
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On Fri, Nov 29, 2019 at 12:37:45PM +1100, 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. Because we can readily catch and > handle this situation, switch to alloc_cpu_gfp and pass in __GFP_NOWARN. > > 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 > Cc: stable@vger.kernel.org # v4.10+ > Signed-off-by: Daniel Axtens <dja@axtens.net> >
So there is a CVE now, but it appears that the patch went nowhere. Are there any plans to actually apply it ?
Thanks, Guenter
> -- > > There's a syz reproducer on the powerpc syzbot that eventually hits > the bug, but it can take up to an hour or so before it keels over on a > kernel with all the syzkaller debugging on, and even longer on a > production kernel. I have been able to reproduce it once on a stock > Ubuntu 5.0 ppc64le kernel. > > I will ask MITRE for a CVE - while only the process doing the syscall > gets killed, it gets killed while holding the relay_channels_mutex, > so it blocks all future relay activity. > --- > kernel/relay.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/relay.c b/kernel/relay.c > index ade14fb7ce2e..a376cc6b54ec 100644 > --- a/kernel/relay.c > +++ b/kernel/relay.c > @@ -580,7 +580,13 @@ struct rchan *relay_open(const char *base_filename, > if (!chan) > return NULL; > > - chan->buf = alloc_percpu(struct rchan_buf *); > + chan->buf = alloc_percpu_gfp(struct rchan_buf *, > + GFP_KERNEL | __GFP_NOWARN); > + if (!chan->buf) { > + kfree(chan); > + return NULL; > + } > + > chan->version = RELAYFS_CHANNEL_VERSION; > chan->n_subbufs = n_subbufs; > chan->subbuf_size = subbuf_size; > -- > 2.20.1 >
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