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SubjectRe: KASAN: use-after-free Read in locks_delete_block
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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@syzkaller.appspotmail.com
> > >
> > > 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@suse.com>
> 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@syzkaller.appspotmail.com
>
> Signed-off-by: NeilBrown <neilb@suse.com>
> ---
> 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@kernel.org>

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