Re: [PATCH] mm/util.c: add a none zero check of "len"

David Rientjes
2015-01-21T23:09:50Z

On Tue, 20 Jan 2015, Pan Xinhui wrote:

> Although this check should have been done by caller. But as it's exported to
> others,
> It's better to add a none zero check of "len" like other functions.
>
> Signed-off-by: xinhuix.pan <xinhuix.pan@intel.com>
> ---
> mm/util.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/util.c b/mm/util.c
> index fec39d4..3dc2873 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -72,6 +72,9 @@ void *kmemdup(const void *src, size_t len, gfp_t gfp)
> {
> void *p;
> + if (unlikely(!len))
> + return ERR_PTR(-EINVAL);
> +
> p = kmalloc_track_caller(len, gfp);
> if (p)
> memcpy(p, src, len);
> @@ -91,6 +94,8 @@ void *memdup_user(const void __user *src, size_t len)
> {
> void *p;
> + if (unlikely(!len))
> + return ERR_PTR(-EINVAL);
> /*
> * Always use GFP_KERNEL, since copy_from_user() can sleep and
> * cause pagefault, which makes it pointless to use GFP_NOFS

Nack, there's no need for this since both slab and slub check for
ZERO_OR_NULL_PTR() and kmalloc_slab() will return ZERO_SIZE_PTR in these
cases. kmemdup() would then return NULL, which is appropriate since it
doesn't return an ERR_PTR() even when memory cannot be allocated.
memdup_user() would return -ENOMEM for size == 0, which would arguably be
the wrong return value, but I don't think we need to slow down either of
these library functions to check for something as stupid as duplicating
size == 0.