Messages in this thread |  | | From | Daniel Axtens <> | | Subject | Re: [PATCH] relay: handle alloc_percpu returning NULL in relay_open | | Date | Tue, 24 Dec 2019 11:26:09 +1100 |
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Guenter Roeck <linux@roeck-us.net> writes:
> 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 ?
I sent a v2 that addresses some review comments, I guess if anything is applied it will be that.
Daniel
> > 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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