linux-kernel - Re: [PATCH] ext4: fix NULL pointer dereference from orig_data in fill

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Message-ID: <CAKYAXd87ry6D4xsBwkXC4at6kDZgHu=_Qa+0kdhEsN=RSMk1ag@mail.gmail.com>
Date:	Mon, 7 Nov 2011 08:13:11 +0900
From:	NamJae Jeon <linkinjeon@...il.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tytso@....edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: fix NULL pointer dereference from orig_data in
 fill_super and remount.

2011/11/7 Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>:
> On 11/06/2011 08:49 PM, Namjae Jeon wrote:
>> Fix NULL pointer dereference from orig_data in fill_super and remount.
>>
>> Signed-off-by: Namjae Jeon <linkinjeon@...il.com>
>> ---
>>  fs/ext4/super.c |   12 ++++++++++--
>>  1 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index 9953d80..3770d3f 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -3102,7 +3102,6 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>                               __releases(kernel_lock)
>>                               __acquires(kernel_lock)
>>  {
>> -     char *orig_data = kstrdup(data, GFP_KERNEL);
>>       struct buffer_head *bh;
>>       struct ext4_super_block *es = NULL;
>>       struct ext4_sb_info *sbi;
>> @@ -3124,6 +3123,10 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>       int err;
>>       unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
>>       ext4_group_t first_not_zeroed;
>> +
>> +     char *orig_data = kstrdup(data, GFP_KERNEL);
>> +     if (!orig_data)
>> +             return ret;
>>
>>       sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
>>       if (!sbi)
>> @@ -4398,6 +4401,10 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>>       int i;
>>  #endif
>>       char *orig_data = kstrdup(data, GFP_KERNEL);
>> +     if (!orig_data) {
>> +             err = -ENOMEM;
>> +             goto failed_alloc_orig;
>
> I didn't quite get why 'failed_alloc_orig' is needed here.
> Why can't we just return -ENOMEM? Anyway we haven't yet
> clobbered any opts at this point, right?
>
> See my comments below.
>
>> +     }
>>
>>       /* Store the original options */
>>       lock_super(sb);
>> @@ -4562,6 +4569,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>>       return 0;
>>
>>  restore_opts:
>> +     kfree(orig_data);
>> +failed_alloc_orig:
>>       sb->s_flags = old_sb_flags;
>>       sbi->s_mount_opt = old_opts.s_mount_opt;
>>       sbi->s_mount_opt2 = old_opts.s_mount_opt2;
>
> This would put garbage values in sb->... and sbi->... when we jump
> to 'failed_alloc_orig' upon 'orig_data' allocation failure, because
> the old_* variables were still uninitialized at that point.
>
>> @@ -4580,7 +4589,6 @@ restore_opts:
>>       }
>>  #endif
>>       unlock_super(sb);
>> -     kfree(orig_data);
>>       return err;
>>  }
>>
>
> Thanks,
> Srivatsa S. Bhat
Hi.
Thanks for your review. It's my mistake.
I will post patch v2 after modifing again.
>
>
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