On 2017-03-27 12:47, Johannes Berg wrote:
> On Fri, 2017-03-24 at 18:06 -0700, Matthias Kaehlcke wrote:
>> __ieee80211_amsdu_copy_frag intentionally initializes a pointer to
>> array[-1] to increment it later to valid values. clang rightfully
>> generates an array-bounds warning on the initialization statement.
>> Work around this by initializing the pointer to array[0] and
>> decrementing it later, which allows to leave the rest of the
>> algorithm untouched.
>>
>> Signed-off-by: Matthias Kaehlcke <m...@chromium.org>
>> ---
>> net/wireless/util.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/wireless/util.c b/net/wireless/util.c
>> index 68e5f2ecee1a..d3d459e4a070 100644
>> --- a/net/wireless/util.c
>> +++ b/net/wireless/util.c
>> @@ -659,7 +659,7 @@ __ieee80211_amsdu_copy_frag(struct sk_buff *skb,
>> struct sk_buff *frame,
>> int offset, int len)
>> {
>> struct skb_shared_info *sh = skb_shinfo(skb);
>> - const skb_frag_t *frag = &sh->frags[-1];
>> + const skb_frag_t *frag = &sh->frags[0];
>> struct page *frag_page;
>> void *frag_ptr;
>> int frag_len, frag_size;
>> @@ -669,6 +669,7 @@ __ieee80211_amsdu_copy_frag(struct sk_buff *skb,
>> struct sk_buff *frame,
>> frag_page = virt_to_head_page(skb->head);
>> frag_ptr = skb->data;
>> frag_size = head_size;
>> + frag--;
>
> Isn't it just a question of time until the compiler will see through
> this trick and warn about it?
Frag is incremented again before being accessed, so there is nothing for
the compiler to see through here.
Acked-by: Felix Fietkau <n...@nbd.name>
- Felix
