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;
Thanks,
Yi.
