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SubjectRe: [PATCH] ata: sata_mv: Fix incorrect string length computation in mv_dump_mem()
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Le 05/09/2023 à 07:04, Damien Le Moal a écrit :
> On 9/5/23 04:54, Christophe JAILLET wrote:
>> snprintf() returns the "number of characters which *would* be generated for
>> the given input", not the size *really* generated.
>>
>> In order to avoid too large values for 'o' (and potential negative values
>> for "sizeof(linebuf) o") use scnprintf() instead of snprintf().
>>
>> Note that given the "w < 4" in the for loop, the buffer can NOT
>> overflow, but using the *right* function is always better.
>>
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>
> Doesn't this need Fixes and CC stable tags ?

I don't think so.
As said in the commit message :
Note that given the "w < 4" in the for loop, the buffer can NOT
overflow, but using the *right* function is always better.

linebuf is 38 chars.
In each iteration, we write 9 bytes + NULL.
We write only 4 elements per line (because of w < 4), so 9 * 4 + 1 = 37
bytes are needed.
9 is for %08x<space>

It can't overflow.
Moreover, it is really unlikely that the size of linebuf or the number
of elements on each line change in a stable kernel.

So, from my POV, this patch is more a clean-up than anything else.

I would even agree that it is maybe not even needed. But should someone
cut'n'paste it one day, then using the correct function could maybe help
him.

CJ

>
>> ---
>> drivers/ata/sata_mv.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
>> index d105db5c7d81..45e48d653c60 100644
>> --- a/drivers/ata/sata_mv.c
>> +++ b/drivers/ata/sata_mv.c
>> @@ -1255,8 +1255,8 @@ static void mv_dump_mem(struct device *dev, void __iomem *start, unsigned bytes)
>>
>> for (b = 0; b < bytes; ) {
>> for (w = 0, o = 0; b < bytes && w < 4; w++) {
>> - o += snprintf(linebuf + o, sizeof(linebuf) - o,
>> - "%08x ", readl(start + b));
>> + o += scnprintf(linebuf + o, sizeof(linebuf) - o,
>> + "%08x ", readl(start + b));
>> b += sizeof(u32);
>> }
>> dev_dbg(dev, "%s: %p: %s\n",
>

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