Re: [PATCH 1/2] of: fdt: fix memory leak in fdt_ensure_space

[Stefan Kerkmann <s.kerkmann@pengutronix.de>]

Hello Ahmad,

On 31.01.24 18:15, Ahmad Fatoum wrote:
> Hello Stefan,
> 
> On 31.01.24 17:56, Stefan Kerkmann wrote:
>> If the reallocation failed the old memory remains allocated and is never
>> freed, this is fixed by freeing the old memory on error.
>>
>> Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
>> ---
>>   drivers/of/fdt.c | 27 ++++++++++++++++++++-------
>>   1 file changed, 20 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> index 5c21bab5de..4f79a6120f 100644
>> --- a/drivers/of/fdt.c
>> +++ b/drivers/of/fdt.c
>> @@ -375,24 +375,37 @@ static void *memalign_realloc(void *orig, size_t oldsize, size_t newsize)
>>   
>>   static int fdt_ensure_space(struct fdt *fdt, int dtsize)
>>   {
>> +	size_t new_size;
>> +	void *previous;
>> +
>>   	/*
>>   	 * We assume strings and names have a maximum length of 1024
>>   	 * whereas properties can be longer. We allocate new memory
>>   	 * if we have less than 1024 bytes (+ the property size left.
>>   	 */
>>   	if (fdt->str_size - fdt->str_nextofs < 1024) {
>> -		fdt->strings = realloc(fdt->strings, fdt->str_size * 2);
>> -		if (!fdt->strings)
>> +		previous = fdt->strings;
>> +		new_size = fdt->str_size * 2;
>> +
>> +		if ((fdt->strings = realloc(previous, new_size)) == NULL) {
> 
> IMO, it's less readable this way. I'd prefer we leave the realloc line and
> then !fdt->strings check on separate lines as before.

Applied.

>> +			free(previous);
> 
> This could happen later in the callers (look for out_free) if one wouldn't
> set fdt->strings to NULL on error. I don't feel strongly either way, so doing
> it this way is fine too.
> 

Freeing the previous memory should happen in this function IMHO. In this 
way `fdt->[strings|dt]` can be set to `NULL` and the caller will get a 
segfaulty reminder if they choose to ignore error returned from the 
function and still access `fdt->[strings|dt]`.

> Change looks good otherwise, so with first comment addressed:
> 

Thank you :-).

> Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> 
> Cheers,
> Ahmad
> 
>>   			return -ENOMEM;
>> -		fdt->str_size *= 2;
>> +		}
>> +
>> +		fdt->str_size = new_size;
>>   	}
>>   
>>   	if (fdt->dt_size - fdt->dt_nextofs < 1024 + dtsize) {
>> -		fdt->dt = memalign_realloc(fdt->dt, fdt->dt_size,
>> -				fdt->dt_size * 2);
>> -		if (!fdt->dt)
>> +		previous = fdt->dt;
>> +		new_size = fdt->dt_size * 2;
>> +
>> +		if ((fdt->dt = memalign_realloc(previous, fdt->dt_size,
>> +						new_size)) == NULL) {
>> +			free(previous);
>>   			return -ENOMEM;
>> -		fdt->dt_size *= 2;
>> +		}
>> +
>> +		fdt->dt_size = new_size;
>>   	}
>>   
>>   	return 0;
>>
> 

Cheers
Stefan

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