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

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Date:   Tue, 20 Sep 2022 09:07:57 +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 2022/9/20 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.
>>               return -ENOMEM;
>> +        state->fc_regions = fc_regions;
>>       }
>>       region = &state->fc_regions[state->fc_regions_used++];
>>       region->ino = ino;
>
> Regards,
>
> Damien
>
> .
>