On Fri, 2016-12-09 at 19:30 +0100, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@xxxxxxxxxxxxxxxxxxxxx>
> Date: Fri, 9 Dec 2016 19:09:13 +0100
>
> The function "kmalloc" was called in one case by the function "sb_equal"
> without checking immediately if it failed.
> This issue was detected by using the Coccinelle software.
>
> Perform the desired memory allocation (and release at the end)
> by a single function call instead.
>
> Fixes: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ("Linux-2.6.12-rc2")
Making a change does not mean fixes.
There's nothing particularly _wrong_ with the code as-is.
2 kmemdup calls might make the code more obvious.
There's a small optimization possible in that only the
first MB_SB_GENERIC_CONSTANT_WORDS of the struct are
actually compared. Alloc and copy of both entire structs
is inefficient and unnecessary.
Perhaps something like the below would be marginally
better/faster, but the whole thing is dubious.
static int sb_equal(mdp_super_t *sb1, mdp_super_t *sb2)
{
int ret;
void *tmp1, *tmp2;
tmp1 = kmemdup(sb1, MD_SB_GENERIC_CONSTANT_WORDS * sizeof(__u32), GFP_KERNEL);
tmp2 = kmemdup(sb2, MD_SB_GENERIC_CONSTANT_WORDS * sizeof(__u32), GFP_KERNEL);
if (!tmp1 || !tmp2) {
ret = 0;
goto out;
}
/*
* nr_disks is not constant
*/
((mdp_super_t *)tmp1)->nr_disks = 0;
((mdp_super_t *)tmp2)->nr_disks = 0;
ret = memcmp(tmp1, tmp2, MD_SB_GENERIC_CONSTANT_WORDS * sizeof(__u32)) == 0;
out:
kfree(tmp1);
kfree(tmp2);
return ret;
}
> Signed-off-by: Markus Elfring <elfring@xxxxxxxxxxxxxxxxxxxxx>
> ---
> drivers/md/md.c | 13 ++++---------
> 1 file changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index b088668269b0..86caf2536255 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -843,15 +843,12 @@ static int sb_equal(mdp_super_t *sb1, mdp_super_t *sb2)
> int ret;
> mdp_super_t *tmp1, *tmp2;
>
> - tmp1 = kmalloc(sizeof(*tmp1),GFP_KERNEL);
> - tmp2 = kmalloc(sizeof(*tmp2),GFP_KERNEL);
> -
> - if (!tmp1 || !tmp2) {
> - ret = 0;
> - goto abort;
> - }
> + tmp1 = kmalloc(2 * sizeof(*tmp1), GFP_KERNEL);
> + if (!tmp1)
> + return 0;
>
> *tmp1 = *sb1;
> + tmp2 = tmp1 + 1;
> *tmp2 = *sb2;
>
> /*
> @@ -861,9 +858,7 @@ static int sb_equal(mdp_super_t *sb1, mdp_super_t *sb2)
> tmp2->nr_disks = 0;
>
> ret = (memcmp(tmp1, tmp2, MD_SB_GENERIC_CONSTANT_WORDS * 4) == 0);
> -abort:
> kfree(tmp1);
> - kfree(tmp2);
> return ret;
> }
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