Re: f2fs: BUG_ON() is triggered when mount valid f2fs filesystem

From: Gu Zheng
Date: Fri Apr 18 2014 - 02:50:29 EST

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Hi Alexey, Kim,
On 04/18/2014 02:04 PM, Alexey Khoroshilov wrote:

> On 17.04.2014 00:45, Jaegeuk Kim wrote:
>> Hi,
>>
>> 2014-04-16 (ì), 18:11 -0700, Alexey Khoroshilov:
>>> Hi,
>>>
>>> But would not ability to trigger BUG_ON by mounting a crafted image
>>> considered as an issue having security implications?
>> Sorry, I can't come up with you.
>> Could you please explain why this can be related to the security hole?
>> Did you mean it needs to avoid such the BUG_ONs if the image has
>> obsolete data being used before?
> An ability to trigger a BUG_ON assert by mounting a crafted image is
> usually considered as a local denial of service [1-3]. As far as I
> understand, the reason is that some kernel data may become inconsistent
> that can lead to further problems.

I think I caught the key point if I do not miss-read it.
Alexey's misgiving is that users can mount a crafted or malicious
image to trigger a BUG_ON, and results in the server panic, especially the
normal user can do this via fuse,user_namespace...
So it seems a leak that the user only mounts an invalid image, but results
in denial of service.
The following 3 cases also show this point.
So the right way may be return the suitable *ERROR* to the user rather than
trigger BUG_ON.

Regards,
Gu

>
> [1] http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-3353
> [2] http://www.openwall.com/lists/oss-security/2011/06/24/4
> [3] http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-2928
> etc.
>
> --
> Alexey
>
>
>> On 16.04.2014 16:35, Jaegeuk Kim wrote:
>>>> Hi,
>>>>
>>>> 2014-04-16 (ì), 13:11 +0400, Andrey Tsyvarev:
>>>>> Hi,
>>>>>
>>>>> With this patch mounting of the image continues to fail (with similar
>>>>> BUG_ON).
>>>>> But when image is formatted again (and steps mentioned in the previous
>>>>> message are performed),
>>>>> mounting of it is now succeed.
>>>>>
>>>>> Is this is a true purpose of the patch?
>>>> Indeed. The patch solves there-in root cause.
>>>> But, if you're trying to use the failed image again, simply you can skip
>>>> the errorneous part by:
>>>>
>>>> # mount ... -o disable_roll_forward ...
>>>>
>>>> Once sync or umount whatever checkpoint is done after that, the image
>>>> will be mounted without "disable_roll_forward".
>>>>
>>>> Thanks,
>>>>
>>>>> 15.04.2014 15:04, Jaegeuk Kim ÐÐÑÐÑ:
>>>>>> Hi,
>>>>>>
>>>>>> Thank you for the report.
>>>>>> I retrieved the fault image and found out that previous garbage data
>>>>>> wreak such the wrong behaviors.
>>>>>> So, I wrote the following patch that fills one zero-block at the
>>>>>> checkpoint procedure.
>>>>>> If the underlying device supports discard, I expect that it mostly
>>>>>> doesn't incur any performance regression significantly.
>>>>>>
>>>>>> Could you test this patch?
>>>>>>
>>>>>> >From 60588ceb7277aae2a79e7f67f5217d1256720d78 Mon Sep 17 00:00:00 2001
>>>>>> From: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>
>>>>>> Date: Tue, 15 Apr 2014 13:57:55 +0900
>>>>>> Subject: [PATCH] f2fs: avoid to conduct roll-forward due to the remained
>>>>>> garbage blocks
>>>>>>
>>>>>> The f2fs always scans the next chain of direct node blocks.
>>>>>> But some garbage blocks are able to be remained due to no discard
>>>>>> support or
>>>>>> SSR triggers.
>>>>>> This occasionally wreaks recovering wrong inodes that were used or
>>>>>> BUG_ONs
>>>>>> due to reallocating node ids as follows.
>>>>>>
>>>>>> When mount this f2fs image:
>>>>>> http://linuxtesting.org/downloads/f2fs_fault_image.zip
>>>>>> BUG_ON is triggered in f2fs driver (messages below are generated on
>>>>>> kernel 3.13.2; for other kernels output is similar):
>>>>>>
>>>>>> kernel BUG at fs/f2fs/node.c:215!
>>>>>> Call Trace:
>>>>>> [<ffffffffa032ebad>] recover_inode_page+0x1fd/0x3e0 [f2fs]
>>>>>> [<ffffffff811446e7>] ? __lock_page+0x67/0x70
>>>>>> [<ffffffff81089990>] ? autoremove_wake_function+0x50/0x50
>>>>>> [<ffffffffa0337788>] recover_fsync_data+0x1398/0x15d0 [f2fs]
>>>>>> [<ffffffff812b9e5c>] ? selinux_d_instantiate+0x1c/0x20
>>>>>> [<ffffffff811cb20b>] ? d_instantiate+0x5b/0x80
>>>>>> [<ffffffffa0321044>] f2fs_fill_super+0xb04/0xbf0 [f2fs]
>>>>>> [<ffffffff811b861e>] ? mount_bdev+0x7e/0x210
>>>>>> [<ffffffff811b8769>] mount_bdev+0x1c9/0x210
>>>>>> [<ffffffffa0320540>] ? validate_superblock+0x210/0x210 [f2fs]
>>>>>> [<ffffffffa031cf8d>] f2fs_mount+0x1d/0x30 [f2fs]
>>>>>> [<ffffffff811b9497>] mount_fs+0x47/0x1c0
>>>>>> [<ffffffff81166e00>] ? __alloc_percpu+0x10/0x20
>>>>>> [<ffffffff811d4032>] vfs_kern_mount+0x72/0x110
>>>>>> [<ffffffff811d6763>] do_mount+0x493/0x910
>>>>>> [<ffffffff811615cb>] ? strndup_user+0x5b/0x80
>>>>>> [<ffffffff811d6c70>] SyS_mount+0x90/0xe0
>>>>>> [<ffffffff8166f8d9>] system_call_fastpath+0x16/0x1b
>>>>>>
>>>>>> Found by Linux File System Verification project (linuxtesting.org).
>>>>>>
>>>>>> Reported-by: Andrey Tsyvarev <tsyvarev@xxxxxxxxx>
>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk.kim@xxxxxxxxxxx>
>>>>>> ---
>>>>>> fs/f2fs/checkpoint.c | 6 ++++++
>>>>>> fs/f2fs/f2fs.h | 1 +
>>>>>> fs/f2fs/segment.c | 17 +++++++++++++++--
>>>>>> 3 files changed, 22 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>>>> index 4aa521a..890e23d 100644
>>>>>> --- a/fs/f2fs/checkpoint.c
>>>>>> +++ b/fs/f2fs/checkpoint.c
>>>>>> @@ -762,6 +762,12 @@ static void do_checkpoint(struct f2fs_sb_info *sbi,
>>>>>> bool is_umount)
>>>>>> void *kaddr;
>>>>>> int i;
>>>>>>
>>>>>> + /*
>>>>>> + * This avoids to conduct wrong roll-forward operations and uses
>>>>>> + * metapages, so should be called prior to sync_meta_pages below.
>>>>>> + */
>>>>>> + discard_next_dnode(sbi);
>>>>>> +
>>>>>> /* Flush all the NAT/SIT pages */
>>>>>> while (get_pages(sbi, F2FS_DIRTY_META))
>>>>>> sync_meta_pages(sbi, META, LONG_MAX);
>>>>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>>>>> index 2ecac83..2c5a5da 100644
>>>>>> --- a/fs/f2fs/f2fs.h
>>>>>> +++ b/fs/f2fs/f2fs.h
>>>>>> @@ -1179,6 +1179,7 @@ int f2fs_issue_flush(struct f2fs_sb_info *);
>>>>>> void invalidate_blocks(struct f2fs_sb_info *, block_t);
>>>>>> void refresh_sit_entry(struct f2fs_sb_info *, block_t, block_t);
>>>>>> void clear_prefree_segments(struct f2fs_sb_info *);
>>>>>> +void discard_next_dnode(struct f2fs_sb_info *);
>>>>>> int npages_for_summary_flush(struct f2fs_sb_info *);
>>>>>> void allocate_new_segments(struct f2fs_sb_info *);
>>>>>> struct page *get_sum_page(struct f2fs_sb_info *, unsigned int);
>>>>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>>>>> index 1e264e7..9993f94 100644
>>>>>> --- a/fs/f2fs/segment.c
>>>>>> +++ b/fs/f2fs/segment.c
>>>>>> @@ -335,13 +335,26 @@ static void locate_dirty_segment(struct
>>>>>> f2fs_sb_info *sbi, unsigned int segno)
>>>>>> mutex_unlock(&dirty_i->seglist_lock);
>>>>>> }
>>>>>>
>>>>>> -static void f2fs_issue_discard(struct f2fs_sb_info *sbi,
>>>>>> +static int f2fs_issue_discard(struct f2fs_sb_info *sbi,
>>>>>> block_t blkstart, block_t blklen)
>>>>>> {
>>>>>> sector_t start = SECTOR_FROM_BLOCK(sbi, blkstart);
>>>>>> sector_t len = SECTOR_FROM_BLOCK(sbi, blklen);
>>>>>> - blkdev_issue_discard(sbi->sb->s_bdev, start, len, GFP_NOFS, 0);
>>>>>> trace_f2fs_issue_discard(sbi->sb, blkstart, blklen);
>>>>>> + return blkdev_issue_discard(sbi->sb->s_bdev, start, len, GFP_NOFS, 0);
>>>>>> +}
>>>>>> +
>>>>>> +void discard_next_dnode(struct f2fs_sb_info *sbi)
>>>>>> +{
>>>>>> + struct curseg_info *curseg = CURSEG_I(sbi, CURSEG_WARM_NODE);
>>>>>> + block_t blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
>>>>>> +
>>>>>> + if (f2fs_issue_discard(sbi, blkaddr, 1)) {
>>>>>> + struct page *page = grab_meta_page(sbi, blkaddr);
>>>>>> + /* zero-filled page */
>>>>>> + set_page_dirty(page);
>>>>>> + f2fs_put_page(page, 1);
>>>>>> + }
>>>>>> }
>>>>>>
>>>>>> static void add_discard_addrs(struct f2fs_sb_info *sbi,
>>>
>
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