On Wed 15 May 2024 12:59:26 PM +08, Zhang Yi wrote;
> On 2024/5/14 21:04, Luis Henriques wrote:
>> On Sat 11 May 2024 02:24:17 PM +08, Zhang Yi wrote;
>>
>>> On 2024/5/10 19:52, Luis Henriques (SUSE) wrote:
>>>> When doing fast_commit replay an infinite loop may occur due to an
>>>> uninitialized extent_status struct. ext4_ext_determine_insert_hole() does
>>>> not detect the replay and calls ext4_es_find_extent_range(), which will
>>>> return immediately without initializing the 'es' variable.
>>>>
>>>> Because 'es' contains garbage, an integer overflow may happen causing an
>>>> infinite loop in this function, easily reproducible using fstest generic/039.
>>>>
>>>> This commit fixes this issue by detecting the replay in function
>>>> ext4_ext_determine_insert_hole(). It also adds initialization code to the
>>>> error path in function ext4_es_find_extent_range().
>>>>
>>>> Thanks to Zhang Yi, for figuring out the real problem!
>>>>
>>>> Fixes: 8016e29f4362 ("ext4: fast commit recovery path")
>>>> Signed-off-by: Luis Henriques (SUSE) <luis.henriques@xxxxxxxxx>
>>>> ---
>>>> Hi!
>>>>
>>>> Two comments:
>>>> 1) The change in ext4_ext_map_blocks() could probably use the min_not_zero
>>>> macro instead. I decided not to do so simply because I wasn't sure if
>>>> that would be safe, but I'm fine changing that if you think it is.
>>>>
>>>> 2) I thought about returning 'EXT_MAX_BLOCKS' instead of '0' in
>>>> ext4_lblk_t ext4_ext_determine_insert_hole(), which would then avoid
>>>> the extra change to ext4_ext_map_blocks(). '0' sounds like the right
>>>> value to return, but I'm also OK using 'EXT_MAX_BLOCKS' instead.
>>>>
>>>> And again thanks to Zhang Yi for pointing me the *real* problem!
>>>>
>>>> fs/ext4/extents.c | 6 +++++-
>>>> fs/ext4/extents_status.c | 5 ++++-
>>>> 2 files changed, 9 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>>> index e57054bdc5fd..b5bfcb6c18a0 100644
>>>> --- a/fs/ext4/extents.c
>>>> +++ b/fs/ext4/extents.c
>>>> @@ -4052,6 +4052,9 @@ static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,
>>>> ext4_lblk_t hole_start, len;
>>>> struct extent_status es;
>>>>
>>>> + if (EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY)
>>>> + return 0;
>>>> +
>>>
>>> Sorry, I think it's may not correct. When replaying the jouranl, although
>>> we don't use the extent statue tree, we still need to query the accurate
>>> hole length, e.g. please see skip_hole(). If you do this, the hole length
>>> becomes incorrect, right?
>>
>> Thank you for your review (and sorry for my delay replying).
>>
>> So, I see three different options to follow your suggestion:
>>
>> 1) Initialize 'es' immediately when declaring it in function
>> ext4_ext_determine_insert_hole():
>>
>> es.es_lblk = es.es_len = es.es_pblk = 0;
>>
>> 2) Initialize 'es' only in ext4_es_find_extent_range() when checking if an
>> fc replay is in progress (my patch was already doing something like
>> that):
>>
>> if (EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY) {
>> /* Initialize extent to zero */
>> es->es_lblk = es->es_len = es->es_pblk = 0;
>> return;
>> }
>>
>> 3) Remove the check for fc replay in function ext4_es_find_extent_range(),
>> which will then unconditionally call __es_find_extent_range(). This
>> will effectively also initialize the 'es' fields to '0' and, because
>> __es_tree_search() will return NULL (at least in generic/039 test!),
>> nothing else will be done.
>>
>> Since all these 3 options seem to have the same result, I believe option
>> 1) is probably the best as it initializes the structure shortly after it's
>> declaration. Would you agree? Or did I misunderstood you?
>>
>
> Both 1 and 2 are looks fine to me, but I would prefer to initialize it
> unconditionally in ext4_es_find_extent_range().
>
> @@ -310,6 +310,8 @@ void ext4_es_find_extent_range(struct inode *inode,
> ext4_lblk_t lblk, ext4_lblk_t end,
> struct extent_status *es)
> {
> + es->es_lblk = es->es_len = es->es_pblk = 0;
> +
> if (EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY)
> return;
Thank you, Yi. I'll send out v2 shortly. Although, to be fair, the real
patch author shouldn't be me. :-)
Cheers,
--
Luis
