On Tue, Nov 13, 2018 at 04:41:56PM +0000, Ben Hutchings wrote:
From: Michal Hocko <mhocko@xxxxxxxx>
commit bb177a732c4369bb58a1fe1df8f552b6f0f7db5f upstream.
syzbot has noticed that a specially crafted library can easily hit
VM_BUG_ON in __mm_populate
kernel BUG at mm/gup.c:1242!
invalid opcode: 0000 [#1] SMP
CPU: 2 PID: 9667 Comm: a.out Not tainted 4.18.0-rc3 #644
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
RIP: 0010:__mm_populate+0x1e2/0x1f0
Code: 55 d0 65 48 33 14 25 28 00 00 00 89 d8 75 21 48 83 c4 20 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 75 18 f1 ff 0f 0b e8 6e 18 f1 ff <0f> 0b 31 db eb c9 e8 93 06 e0 ff 0f 1f 00 55 48 89 e5 53 48 89 fb
Call Trace:
vm_brk_flags+0xc3/0x100
vm_brk+0x1f/0x30
load_elf_library+0x281/0x2e0
__ia32_sys_uselib+0x170/0x1e0
do_fast_syscall_32+0xca/0x420
entry_SYSENTER_compat+0x70/0x7f
The reason is that the length of the new brk is not page aligned when we
try to populate the it. There is no reason to bug on that though.
do_brk_flags already aligns the length properly so the mapping is
expanded as it should. All we need is to tell mm_populate about it.
Besides that there is absolutely no reason to to bug_on in the first
place. The worst thing that could happen is that the last page wouldn't
get populated and that is far from putting system into an inconsistent
state.
Fix the issue by moving the length sanitization code from do_brk_flags
up to vm_brk_flags. The only other caller of do_brk_flags is brk
syscall entry and it makes sure to provide the proper length so t here
is no need for sanitation and so we can use do_brk_flags without it.
Also remove the bogus BUG_ONs.
[osalvador@xxxxxxxxxxxxxxxxxx: fix up vm_brk_flags s@request@len@]
Link: http://lkml.kernel.org/r/20180706090217.GI32658@xxxxxxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reported-by: syzbot <syzbot+5dcb560fe12aa5091c06@xxxxxxxxxxxxxxxxxxxxxxxxx>
Tested-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[bwh: Backported to 4.9:
- There is no do_brk_flags() function; update do_brk()
- Adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Queued for 4.9, thank you.
--
Thanks,
Sasha
