Re: [PATCH v2] edac: edac_mc_sysfs.c: Use strlcpy to Copy a C-string into a sized buffer

From: Borislav Petkov
Date: Sun May 28 2017 - 14:12:56 EST


On Fri, May 26, 2017 at 09:10:21PM +0200, Karim Eshapa wrote:
> Use strlcpy with sized buffer instead of strncpy to
> avoid non NUL-terminated source strings problems.

Huh? But it does get terminated.

> Signed-off-by: Karim Eshapa <karim.eshapa@xxxxxxxxx>
> ---
> drivers/edac/edac_mc_sysfs.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/edac/edac_mc_sysfs.c b/drivers/edac/edac_mc_sysfs.c
> index 445862d..e893b94 100644
> --- a/drivers/edac/edac_mc_sysfs.c
> +++ b/drivers/edac/edac_mc_sysfs.c
> @@ -251,8 +251,7 @@ static ssize_t channel_dimm_label_store(struct device *dev,
> if (copy_count == 0 || copy_count >= sizeof(rank->dimm->label))
> return -EINVAL;
>
> - strncpy(rank->dimm->label, data, copy_count);
> - rank->dimm->label[copy_count] = '\0';
> + strlcpy(rank->dimm->label, data, copy_count);
>
> return count;
> }
> @@ -530,8 +529,7 @@ static ssize_t dimmdev_label_store(struct device *dev,
> if (copy_count == 0 || copy_count >= sizeof(dimm->label))
> return -EINVAL;
>
> - strncpy(dimm->label, data, copy_count);
> - dimm->label[copy_count] = '\0';
> + strlcpy(dimm->label, data, copy_count);

Did you try your patch before sending it?

# cat /sys/devices/system/edac/mc/mc0/dimm0/dimm_label
CPU_SrcID#0_Ha#0_Chan#0_DIMM#0
# echo "bla" > /sys/devices/system/edac/mc/mc0/dimm0/dimm_label
# cat /sys/devices/system/edac/mc/mc0/dimm0/dimm_label
bl
# echo "bla boom" > /sys/devices/system/edac/mc/mc0/dimm0/dimm_label
# cat /sys/devices/system/edac/mc/mc0/dimm0/dimm_label
bla boo

Also, I don't like the fact that strlcpy does not pad the remainder of
the dest buffer with NUL.

So unless you're seeing a real bug, please don't waste your time with
this. There are enough real bugs in the kernel which need fixing.

Thanks.

--
Regards/Gruss,
Boris.

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