linux-kernel - Re: [syzbot] KASAN: slab-out-of-bounds Read in ext4_enable

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Message-ID: <8c3757ae-1aeb-49a4-47af-598d1d4737ea@redhat.com>
Date:   Mon, 14 Nov 2022 11:21:33 -0500
From:   Waiman Long <longman@...hat.com>
To:     Theodore Ts'o <tytso@....edu>,
        syzbot <syzbot+ea70429cd5cf47ba8937@...kaller.appspotmail.com>
Cc:     adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        nathan@...nel.org, ndesaulniers@...gle.com,
        syzkaller-bugs@...glegroups.com, trix@...hat.com,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [syzbot] KASAN: slab-out-of-bounds Read in ext4_enable_quotas

On 11/14/22 10:16, Theodore Ts'o wrote:
> +jaeguk,chao,peterz,mingo,longman,boqun.feng (F2FS and Lockdep maintainers)
>
> On Sun, Nov 13, 2022 at 02:55:47PM -0800, syzbot wrote:
>> syzbot has found a reproducer for the following issue on:
>>
>> HEAD commit:    af7a05689189 Merge tag 'mips-fixes_6.1_1' of git://git.ker..
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=175bb059880000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=cbbe7c32024f5b72
>> dashboard link: https://syzkaller.appspot.com/bug?extid=ea70429cd5cf47ba8937
>> compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10930249880000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11af96ae880000
> This looks like it's either a f2fs or lockdep bug.  To trigger the
> crash, the reproducer is mounting and unmounting the f2fs file system
> a huge number of times, and then ext4 calls lockdep_set_subclass which
> then triggers a KASAN report:
>
> BUG: KASAN: slab-out-of-bounds in lockdep_set_quota_inode fs/ext4/super.c:6803 [inline]
>
> On fs/ext4/super.c:6803 is the call to lockdep_set_subclass:
>
> 	lockdep_set_subclass(&ei->i_data_sem, subclass);
>
> So the KASAN failure is coming from some kind of out-of-bounds pointer
> dereference inside lockdep's internal data structures:
>
>   kasan_report+0xcd/0x100 mm/kasan/report.c:495
>   lockdep_set_quota_inode fs/ext4/super.c:6803 [inline]
>   ext4_quota_enable fs/ext4/super.c:6913 [inline]
>   ext4_enable_quotas+0x577/0xcf0 fs/ext4/super.c:6940
>   __ext4_fill_super fs/ext4/super.c:5500 [inline]
>   ext4_fill_super+0x7ee4/0x8610 fs/ext4/super.c:5643
>   get_tree_bdev+0x400/0x620 fs/super.c:1324
>   vfs_get_tree+0x88/0x270 fs/super.c:1531
>   do_new_mount+0x289/0xad0 fs/namespace.c:3040
>   do_mount fs/namespace.c:3383 [inline]

lockdep_set_subclass() should be translated into a call to 
lockdep_init_map_type():

#define lockdep_set_subclass(lock, sub)                                 \
         lockdep_init_map_type(&(lock)->dep_map, #lock, 
(lock)->dep_map.key, sub,\
(lock)->dep_map.wait_type_inner,          \
(lock)->dep_map.wait_type_outer,          \
                               (lock)->dep_map.lock_type)

All memory access should be within the bound of the given 
"&ei->i_data_sem". Also lockdep_init_map_type() is not in the stack 
trace. So it is not a problem within this lockdep_init_map_type() 
function. So is it possible that the given inode pointer is invalid?

Cheers,
Longman