linux-kernel - Re: [PATCH -next 1/2] ext4: fix potential memory leak in ext4_fc_record

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Date:   Wed, 21 Sep 2022 09:26:13 +0800
From:   yebin <yebin10@...wei.com>
To:     Damien Guibouret <damien.guibouret@...tition-saving.com>,
        <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <jack@...e.cz>
Subject: Re: [PATCH -next 1/2] ext4: fix potential memory leak in
 ext4_fc_record_regions()



On 2022/9/21 2:25, Damien Guibouret wrote:
> Hello,
>
> Le 20/09/2022 à 03:07, yebin a écrit :
>>
>>
>> On 2022/9/20 2:40, Damien Guibouret wrote:
>>> Hello,
>>>
>>> Le 19/09/2022 à 16:40, Ye Bin a écrit :
>>>> As krealloc may return NULL, in this case 'state->fc_regions' may 
>>>> not be
>>>> freed by krealloc, but 'state->fc_regions' already set NULL. Then will
>>>> lead to 'state->fc_regions' memory leak.
>>>>
>>>> Signed-off-by: Ye Bin <yebin10@...wei.com>
>>>> ---
>>>>   fs/ext4/fast_commit.c | 14 ++++++++------
>>>>   1 file changed, 8 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
>>>> index 9217a588afd1..cc8c8db075ba 100644
>>>> --- a/fs/ext4/fast_commit.c
>>>> +++ b/fs/ext4/fast_commit.c
>>>> @@ -1677,15 +1677,17 @@ int ext4_fc_record_regions(struct 
>>>> super_block *sb, int ino,
>>>>       if (replay && state->fc_regions_used != state->fc_regions_valid)
>>>>           state->fc_regions_used = state->fc_regions_valid;
>>>>       if (state->fc_regions_used == state->fc_regions_size) {
>>>> +        struct ext4_fc_alloc_region *fc_regions;
>>>> +
>>>>           state->fc_regions_size +=
>>>>               EXT4_FC_REPLAY_REALLOC_INCREMENT;
>>>> -        state->fc_regions = krealloc(
>>>> -                    state->fc_regions,
>>>> -                    state->fc_regions_size *
>>>> -                    sizeof(struct ext4_fc_alloc_region),
>>>> -                    GFP_KERNEL);
>>>> -        if (!state->fc_regions)
>>>> +        fc_regions = krealloc(state->fc_regions,
>>>> +                      state->fc_regions_size *
>>>> +                      sizeof(struct ext4_fc_alloc_region),
>>>> +                      GFP_KERNEL);
>>>> +        if (!fc_regions)
>>>
>>> Would it not be safer to restore state->fc_regions_size to its 
>>> previous value in that case to keep consistency between size value 
>>> and allocated size (or to update state->fc_regions_size only after 
>>> allocation as it is done in second part of this patch) ?
>>>
>> Actually, If   'ext4_fc_record_regions()' return -ENOMEM, then will 
>> stop replay journal.
>> 'state->fc_regions_size' will not be used any more, so it's safe.
>
> There are at least two calls in ext4_ext_clear_bb (ext4/extents.c) 
> that do not check for return code of ext4_fc_record_regions. But 
> perhaps these are these calls that should be fixed.
>
Thanks very much,
Indeed, it's better to repair it here.
>>>>               return -ENOMEM;
>>>> +        state->fc_regions = fc_regions;
>>>>       }
>>>>       region = &state->fc_regions[state->fc_regions_used++];
>>>>       region->ino = ino;
>>>
>
> Regards,
>
> Damien
>
>
> .
>