Re: KASAN: slab-out-of-bounds Read in bpf_csum_update

[Daniel Borkmann]

On 06/04/2018 07:36 AM, Dmitry Vyukov wrote:
> On Mon, Jun 4, 2018 at 1:36 AM, syzbot
> <syzbot+efae31b384d5badbd620@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    0512e0134582 Merge tag 'xfs-4.17-fixes-3' of git://git.ker..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=17eb2d7b800000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=968b0b23c7854c0b
>> dashboard link: https://syzkaller.appspot.com/bug?extid=efae31b384d5badbd620
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=162c6def800000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14fe3db7800000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+efae31b384d5badbd620@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> random: sshd: uninitialized urandom read (32 bytes read)
>> random: sshd: uninitialized urandom read (32 bytes read)
>> random: sshd: uninitialized urandom read (32 bytes read)
>> random: sshd: uninitialized urandom read (32 bytes read)
>> ==================================================================
>> BUG: KASAN: slab-out-of-bounds in ____bpf_csum_update net/core/filter.c:1679
>> [inline]
>> BUG: KASAN: slab-out-of-bounds in bpf_csum_update+0xb4/0xc0
>> net/core/filter.c:1673
>> Read of size 1 at addr ffff8801d9235b50 by task syz-executor507/4513
>>
>> CPU: 0 PID: 4513 Comm: syz-executor507 Not tainted 4.17.0-rc7+ #78
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>>  kasan_report_error mm/kasan/report.c:354 [inline]
>>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>>  __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
>>  ____bpf_csum_update net/core/filter.c:1679 [inline]
>>  bpf_csum_update+0xb4/0xc0 net/core/filter.c:1673
> 
> /\/\/\/\/\
> 
> Are there any known bugs with unwind through bpf functions?

Looks like you don't have kallsyms export enabled, here's a syzkaller diff
to get jit images exposed, then it should work:

diff --git a/tools/create-image.sh b/tools/create-image.sh
index 9f82482..395a2a0 100755
--- a/tools/create-image.sh
+++ b/tools/create-image.sh
@@ -23,6 +23,7 @@ echo 'SELINUX=disabled' | sudo tee $DIR/etc/selinux/config
 echo "kernel.printk = 7 4 1 3" | sudo tee -a $DIR/etc/sysctl.conf
 echo 'debug.exception-trace = 0' | sudo tee -a $DIR/etc/sysctl.conf
 echo "net.core.bpf_jit_enable = 1" | sudo tee -a $DIR/etc/sysctl.conf
+echo "net.core.bpf_jit_kallsyms = 1" | sudo tee -a $DIR/etc/sysctl.conf
 echo "kernel.softlockup_all_cpu_backtrace = 1" | sudo tee -a $DIR/etc/sysctl.conf
 echo "kernel.kptr_restrict = 0" | sudo tee -a $DIR/etc/sysctl.conf
 echo "kernel.watchdog_thresh = 60" | sudo tee -a $DIR/etc/sysctl.conf

Cheers,
Daniel