On Sat, Feb 6, 2016 at 9:18 PM, Jeremiah Mahler <jmmah...@gmail.com> wrote:
> Andrew,
>
> On Fri, Feb 05, 2016 at 02:19:40PM -0800, Andrew Morton wrote:
>> On Fri, 5 Feb 2016 10:05:02 -0800 Jeremiah Mahler <jmmah...@gmail.com> wrote:
>>
> [...]
>> > unable to handle kernel NULL pointer dereference
>>
>> This should fix it up.
>>
> [...]
>>
>> include/linux/radix-tree.h | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff -puN
>> include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry
>> include/linux/radix-tree.h
>> ---
>> a/include/linux/radix-tree.h~radix-tree-fix-oops-after-radix_tree_iter_retry
>> +++ a/include/linux/radix-tree.h
>> @@ -400,7 +400,7 @@ void **radix_tree_iter_retry(struct radi
>> * @iter: pointer to radix tree iterator
>> * Returns: current chunk size
>> */
>> -static __always_inline unsigned
>> +static __always_inline long
>> radix_tree_chunk_size(struct radix_tree_iter *iter)
>> {
>> return iter->next_index - iter->index;
>> @@ -434,9 +434,9 @@ radix_tree_next_slot(void **slot, struct
>> return slot + offset + 1;
>> }
>> } else {
>> - unsigned size = radix_tree_chunk_size(iter) - 1;
>> + long size = radix_tree_chunk_size(iter);
>>
>> - while (size--) {
>> + while (--size > 0) {
>> slot++;
>> iter->index++;
>> if (likely(*slot))
>> _
>>
>
> I have applied this patch to my kernel and so far the bug has not
> come back. Thanks for the quick fix.
>
> Although I don't quite understand how this fixes the slot==NULL problem.
> Unless I am missing something, it looks like the while loop will be
> executed the same number of times but the size variable will no
> longer go negative as it did before.
That's simple. Slot is dereferenced after checking remaining size.
Old version checked only for != 0. After iter-retry size is zero and
afrer "- 1" it overlaps into positive range. In new version it's signed and
checked for > 0.
>
> --
> - Jeremiah Mahler
