syzbot


KASAN: use-after-free Read in skb_ensure_writable

Status: fixed on 2018/07/09 18:05
Subsystems: bpf net
[Documentation on labels]
Reported-by: syzbot+c8504affd4fdd0c1b626@syzkaller.appspotmail.com
Fix commit: 58990d1ff3f7 bpf: reject passing modified ctx to helper functions
First crash: 2177d, last: 2169d
Discussions (4)
Title Replies (including bot) Last reply
[PATCH 4.14 00/62] 4.14.164-stable review 66 (66) 2020/01/13 15:47
[PATCH 4.17 00/67] 4.17.7-stable review 74 (74) 2018/07/17 09:41
KASAN: use-after-free Read in skb_ensure_writable 1 (2) 2018/06/08 09:53
[PATCH bpf] bpf: reject passing modified ctx to helper functions 4 (4) 2018/06/07 19:43

Sample crash report:
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: use-after-free in pskb_may_pull include/linux/skbuff.h:2108 [inline]
BUG: KASAN: use-after-free in skb_ensure_writable+0x554/0x620 net/core/skbuff.c:5118
Read of size 4 at addr ffff8801b0b40fc0 by task syz-executor258/4479

CPU: 0 PID: 4479 Comm: syz-executor258 Not tainted 4.17.0-rc6+ #29
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_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 pskb_may_pull include/linux/skbuff.h:2108 [inline]
 skb_ensure_writable+0x554/0x620 net/core/skbuff.c:5118
 __bpf_try_make_writable net/core/filter.c:1606 [inline]
 bpf_try_make_writable net/core/filter.c:1612 [inline]
 ____bpf_l3_csum_replace net/core/filter.c:1774 [inline]
 bpf_l3_csum_replace+0x8c/0x4d0 net/core/filter.c:1765

The buggy address belongs to the page:
page:ffffea0006c2d000 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: ffffea00075ea760 ffffea0006c39660 ffff8801b5848738 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b0b40e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8801b0b40f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8801b0b40f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                           ^
 ffff8801b0b41000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b0b41080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2018/06/02 05:01 bpf-next bcece5dc40b9 2f93b54f .config console log report syz C ci-upstream-bpf-next-kasan-gce
2018/06/10 16:55 bpf-next 75d4e704fa8d 866118af .config console log report ci-upstream-bpf-next-kasan-gce
2018/06/05 01:43 bpf-next 34ea38ca2799 a50d873b .config console log report ci-upstream-bpf-next-kasan-gce
2018/06/03 02:36 bpf-next 25c1013e0464 2f93b54f .config console log report ci-upstream-bpf-next-kasan-gce
* Struck through repros no longer work on HEAD.