Re: [f2fs-dev] [PATCH -next] f2fs: fix use after free in f2fs_fill_super

[Chao Yu <chao@kernel.org>]

On 2021/7/23 10:41, Jack Qiu wrote:
> On 2021/7/22 22:05, Chao Yu wrote:
>> On 2021/7/22 12:41, Jack Qiu wrote:
>>> The root cause is shrink_dcache_sb after sbi has been freed.
>>> So call shrink_dcache_sb before free sbi and other resources.
>>>
>>> ==================================================================
>>> BUG: KASAN: use-after-free in f2fs_evict_inode+0x31c/0xde5
>>> Read of size 4 at addr ffff8881d97f0d50 by task syz-executor.3/8729
>>>
>>> PU: 1 PID: 8729 Comm: syz-executor.3 Not tainted
>>> 4.19.195-00002-g67dceea04431-dirty #31
>>
>> Does this bug below to 4.19.195?

I mean whether this bug exists in mainline? Not sure, I just doubt maybe
we have fixed this issue, but forgot to backport it to 4.19 stable kernel.

>>
> Yes, I believe ed2e621a95d704e6a4e904cc00524e8cbddda0c2 causes this bug.
> 
> git describe --contains ed2e621a95d704e6a4e904cc00524e8cbddda0c2
> v3.17-rc4~27^2~17
> 
> @@ -1126,6 +1130,13 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>          brelse(raw_super_buf);
>   free_sbi:
>          kfree(sbi);    ---  free sbi
> +
> +       /* give only one another chance */
> +       if (retry) {
> +               retry = !retry;
> +               shrink_dcache_sb(sb); --- call f2fs_evict_inode(root inode), it will access sbi
> +               goto try_onemore;
> +       }
>          return err;
>   }
> 
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>>> ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31
>>> 04/01/2014
>>> Call Trace:
>>>    dump_stack+0xe5/0x14b
>>>    ? f2fs_evict_inode+0x31c/0xde5
>>>    print_address_description+0x6c/0x237
>>>    ? f2fs_evict_inode+0x31c/0xde5
>>>    kasan_report.cold+0x88/0x2a3
>>>    f2fs_evict_inode+0x31c/0xde5
>>>    ? full_proxy_open.cold+0x12/0x12
>>>    evict+0x2cd/0x5f0
>>>    iput+0x3d9/0x6f0
>>>    dentry_unlink_inode+0x273/0x330
>>>    __dentry_kill+0x340/0x5e0
>>>    dentry_kill+0xb7/0x740
>>>    shrink_dentry_list+0x256/0x660
>>>    shrink_dcache_sb+0x11f/0x1d0
>>>    ? shrink_dentry_list+0x660/0x660
>>>    ? __kasan_slab_free+0x144/0x180
>>>    f2fs_fill_super+0x2a34/0x4a80
>>>    ? f2fs_sanity_check_ckpt.cold+0x2b6/0x2b6
>>>    ? wait_for_completion+0x3c0/0x3c0
>>>    ? set_blocksize+0x230/0x2b0
>>>    mount_bdev+0x2c1/0x370
>>>    ? f2fs_sanity_check_ckpt.cold+0x2b6/0x2b6
>>>    mount_fs+0x4c/0x1c0
>>>    vfs_kern_mount.part.0+0x60/0x3d0
>>>    do_mount+0x367/0x2570
>>>    ? kasan_unpoison_shadow+0x33/0x40
>>>    ? copy_mount_string+0x40/0x40
>>>    ? kmem_cache_alloc_trace+0x13f/0x2b0
>>>    ? _copy_from_user+0x94/0x100
>>>    ? copy_mount_options+0x1f1/0x2e0
>>>    ksys_mount+0xa0/0x100
>>>    __x64_sys_mount+0xbf/0x160
>>>    do_syscall_64+0xc2/0x190
>>>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>> RIP: 0033:0x47938e
>>> Code: 48 c7 c1 b4 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84
>>> 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01
>>> f0 ff ff 73 01 c3 48 c7 c1 b4 ff ff ff f7 d8 64 89 01 48
>>> RSP: 002b:00007fed673b6a48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
>>> RAX: ffffffffffffffda RBX: 0000000020000200 RCX: 000000000047938e
>>> RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007fed673b6aa0
>>> RBP: 00007fed673b6ae0 R08: 00007fed673b6ae0 R09: 0000000020000000
>>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000020000000
>>> R13: 0000000020000100 R14: 00007fed673b6aa0 R15: 0000000020000b00
>>>
>>> Allocated by task 8729:
>>>    kasan_kmalloc+0xc2/0xe0
>>>    kmem_cache_alloc_trace+0x13f/0x2b0
>>>    f2fs_fill_super+0x124/0x4a80
>>>    mount_bdev+0x2c1/0x370
>>>    mount_fs+0x4c/0x1c0
>>>    vfs_kern_mount.part.0+0x60/0x3d0
>>>    do_mount+0x367/0x2570
>>>    ksys_mount+0xa0/0x100
>>>    __x64_sys_mount+0xbf/0x160
>>>    do_syscall_64+0xc2/0x190
>>>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> Freed by task 8729:
>>>    __kasan_slab_free+0x12f/0x180
>>>    kfree+0xfa/0x2a0
>>>    f2fs_fill_super+0x2a00/0x4a80
>>>    mount_bdev+0x2c1/0x370
>>>    mount_fs+0x4c/0x1c0
>>>    vfs_kern_mount.part.0+0x60/0x3d0
>>>    do_mount+0x367/0x2570
>>>    ksys_mount+0xa0/0x100
>>>    __x64_sys_mount+0xbf/0x160
>>>    do_syscall_64+0xc2/0x190
>>>    entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> Signed-off-by: Jack Qiu <jack.qiu@huawei.com>
>>> ---
>>>    fs/f2fs/super.c | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index 8fecd3050ccd..b041625e06ce 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -4229,6 +4229,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>    free_compress_inode:
>>>        f2fs_destroy_compress_inode(sbi);
>>>    free_root_inode:
>>> +    if (retry_cnt > 0 && skip_recovery)
>>> +        shrink_dcache_sb(sb);
>>
>> Compare to 4.19, last f2fs adds evict_inodes() before f2fs_unregister_sysfs(),
> Can not find *evict_inodes*, could you please elaborate more detail?

Could you please check whether below patch can fix this issue?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=812a95977fd2f0d1f220c716a98

Thanks,

>> could you please check whether this can fix the issue?
> I have run the test more than 1 day w/ this patch, it will fail in 1 hour before.
> I believe this patch can fix *this* issue. But I'm not quite familiar with shrink_dcache_sb,
> maybe I miss other scenario. If you have other comment, please let me know.
> 
> Thanks,
>>
>> Thanks,
>>
>>>        dput(sb->s_root);
>>>        sb->s_root = NULL;
>>>    free_node_inode:
>>> @@ -4285,7 +4287,6 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>        /* give only one another chance */
>>>        if (retry_cnt > 0 && skip_recovery) {
>>>            retry_cnt--;
>>> -        shrink_dcache_sb(sb);
>>>            goto try_onemore;
>>>        }
>>>        return err;
>>> -- 
>>> 2.17.1
>>>
>> .
> 


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