Re: KASAN: use-after-free Read in locks_delete_block
From: Dmitry Vyukov
Date: Thu Nov 15 2018 - 17:45:39 EST
On Wed, Nov 14, 2018 at 2:36 AM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> On Wed, 2018-11-14 at 07:40 +1100, NeilBrown wrote:
>> On Tue, Nov 13 2018, Jeff Layton wrote:
>>
>> > On Mon, 2018-11-12 at 12:34 -0800, syzbot wrote:
>> > > Hello,
>> > >
>> > > syzbot found the following crash on:
>> > >
>> > > HEAD commit: 442b8cea2477 Add linux-next specific files for 20181109
>> > > git tree: linux-next
>> > > console output: https://syzkaller.appspot.com/x/log.txt?x=115dbad5400000
>> > > kernel config: https://syzkaller.appspot.com/x/.config?x=2f72bdb11df9fbe8
>> > > dashboard link: https://syzkaller.appspot.com/bug?extid=a4a3d526b4157113ec6a
>> > > compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>> > >
>> > > Unfortunately, I don't have any reproducer for this crash yet.
>> > >
>> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > > Reported-by: syzbot+a4a3d526b4157113ec6a@xxxxxxxxxxxxxxxxxxxxxxxxx
/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
Hi Neil,
Please include the Reported-by tag next time.
I see the linux-next patch is already update,
so let's tell syzbot that this is fixed here:
#syz fix: fs/locks: always delete_block after waiting.
If the bug is still open on syzbot dashboard:
https://syzkaller.appspot.com#upstream
syzbot will not report new bugs in these functions in future.
Thanks
>> > > device loop0 blocksize: 4096
>> > > __find_get_block_slow() failed. block=1, b_blocknr=8
>> > > b_state=0x00000029, b_size=512
>> > > device loop0 blocksize: 4096
>> > > ==================================================================
>> > > BUG: KASAN: use-after-free in __list_del_entry_valid+0xf1/0x100
>> > > lib/list_debug.c:51
>> > > Read of size 8 at addr ffff88017eb47b70 by task syz-executor3/13461
>> > >
>> > > CPU: 0 PID: 13461 Comm: syz-executor3 Not tainted 4.20.0-rc1-next-20181109+
>> > > #110
>> > > 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+0x244/0x39d lib/dump_stack.c:113
>> > > print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
>> > > kasan_report_error mm/kasan/report.c:354 [inline]
>> > > kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
>> > > __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>> > > __list_del_entry_valid+0xf1/0x100 lib/list_debug.c:51
>> > > __list_del_entry include/linux/list.h:117 [inline]
>> > > list_del_init include/linux/list.h:159 [inline]
>> > > __locks_delete_block fs/locks.c:683 [inline]
>> > > locks_delete_block+0xce/0x3d0 fs/locks.c:716
>> > > locks_mandatory_area+0x48b/0x6a0 fs/locks.c:1398
>> > > rw_verify_area+0x2f2/0x360 fs/read_write.c:386
>> > > vfs_write+0x149/0x560 fs/read_write.c:544
>> > > ksys_write+0x101/0x260 fs/read_write.c:598
>> > > __do_sys_write fs/read_write.c:610 [inline]
>> > > __se_sys_write fs/read_write.c:607 [inline]
>> > > __x64_sys_write+0x73/0xb0 fs/read_write.c:607
>> > > do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>> > > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> > > RIP: 0033:0x457569
>> > > Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
>> > > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
>> > > ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
>> > > RSP: 002b:00007ff2e8194c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
>> > > RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
>> > > RDX: 0000000000000010 RSI: 0000000020000180 RDI: 0000000000000006
>> > > RBP: 000000000072c0e0 R08: 0000000000000000 R09: 0000000000000000
>> > > R10: 0000000000000000 R11: 0000000000000246 R12: 00007ff2e81956d4
>> > > R13: 00000000004c571f R14: 00000000004d9360 R15: 00000000ffffffff
>> > >
>> > > The buggy address belongs to the page:
>> > > page:ffffea0005fad1c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
>> > > flags: 0x2fffc0000000000()
>> > > raw: 02fffc0000000000 0000000000000000 ffffea0005fad1c8 0000000000000000
>> > > raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
>> > > page dumped because: kasan: bad access detected
>> > >
>> > > Memory state around the buggy address:
>> > > ffff88017eb47a00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> > > ffff88017eb47a80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> > > > ffff88017eb47b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> > >
>> > > ^
>> > > ffff88017eb47b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> > > ffff88017eb47c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>> > > ==================================================================
>> > >
>> >
>> > Ouch, crash down in the mandatory locking code. This is with Neil's set
>> > from last week. I haven't merged the series he sent the other day yet,
>> > but they don't seem to be different in this regard.
>> >
>> > Looks like the fl_blocked list might have had an entry on it that was
>> > freed without being removed? locks_mandatory_area declares a file_lock
>> > on the stack, but it seems to be initialized properly.
>> >
>> > The one weird thing is that locks_mandatory_area sets FL_ACCESS and
>> > FL_SLEEP, but I don't see anything wrong with that right offhand.
>> >
>> > Neil, any thoughts?
>>
>> I'm not certain, but probably this:
>>
>> From: NeilBrown <neilb@xxxxxxxx>
>> Date: Wed, 14 Nov 2018 07:38:05 +1100
>> Subject: [PATCH] fs/locks: always delete_block after waiting - mandatory locks
>>
>> The patch
>> fs/locks: always delete_block after waiting.
>> should have moved the locks_delete_block() call in
>> locks_mandatory_area() too.
>>
>> This might fix the bug:
>> Reported-by: syzbot+a4a3d526b4157113ec6a@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
>> ---
>> fs/locks.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/locks.c b/fs/locks.c
>> index f456cd3d9d50..eb0c0b33fb7b 100644
>> --- a/fs/locks.c
>> +++ b/fs/locks.c
>> @@ -1436,9 +1436,9 @@ int locks_mandatory_area(struct inode *inode, struct file *filp, loff_t start,
>> continue;
>> }
>>
>> - locks_delete_block(&fl);
>> break;
>> }
>> + locks_delete_block(&fl);
>>
>> return error;
>> }
>
> That makes sense. I went ahead and squashed this patch into the earlier
> one and pushed the result to my locks-next branch. linux-next should
> pick it up soon.
>
> Thanks!
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
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