linux-ext4 - Re: [PATCH] ext4: fix potential use after free in __ext4_journal

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Date:	Mon, 5 Oct 2015 13:20:52 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Lukáš Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix potential use after free in __ext4_journal_stop


> On Oct 5, 2015, at 8:18 AM, Lukáš Czerner <lczerner@...hat.com> wrote:
> 
> On Wed, 2 Sep 2015, Lukas Czerner wrote:
> 
>> Date: Wed,  2 Sep 2015 16:45:54 +0200
>> From: Lukas Czerner <lczerner@...hat.com>
>> To: linux-ext4@...r.kernel.org
>> Cc: Lukas Czerner <lczerner@...hat.com>
>> Subject: [PATCH] ext4: fix potential use after free in __ext4_journal_stop
>> 
>> There is a use-after-free possibility in __ext4_journal_stop() in the
>> case that we free the handle in the first jbd2_journal_stop() because
>> we're referencing handle->h_err afterwards. This was introduced in
>> 9705acd63b125dee8b15c705216d7186daea4625 and it is wrong. Fix it by
>> storing the handle->h_err value beforehand and avoid referencing
>> potentially freed handle.
> 
> ping
>> 
>> Signed-off-by: Lukas Czerner <lczerner@...hat.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

>> ---
>> fs/ext4/ext4_jbd2.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
>> index d418431..e770c1ee 100644
>> --- a/fs/ext4/ext4_jbd2.c
>> +++ b/fs/ext4/ext4_jbd2.c
>> @@ -88,13 +88,13 @@ int __ext4_journal_stop(const char *where, unsigned int line, handle_t *handle)
>> 		return 0;
>> 	}
>> 
>> +	err = handle->h_err;
>> 	if (!handle->h_transaction) {
>> -		err = jbd2_journal_stop(handle);
>> -		return handle->h_err ? handle->h_err : err;
>> +		rc = jbd2_journal_stop(handle);
>> +		return err ? err : rc;
>> 	}
>> 
>> 	sb = handle->h_transaction->t_journal->j_private;
>> -	err = handle->h_err;
>> 	rc = jbd2_journal_stop(handle);
>> 
>> 	if (!err)
>> 
> --
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Cheers, Andreas






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