Re: [PATCH] ata: sata_mv: Fix incorrect string length computation in mv_dump_mem()

[Christophe JAILLET]

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@xxxxxxxxxx>
>
> 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",