On Tue, 23 Jul 2019 15:40:20 +0200,
Jia-Ju Bai wrote:
>
> In snd_gf1_mem_xfree(), there is an if statement on line 72 and line 74
> to check whether block->next is NULL:
> if (block->next)
>
> When block->next is NULL, block->next is used on line 84:
> block->next->prev = block->prev;
>
> Thus, a possible null-pointer dereference may occur in this case.
There is already a check beforehand:
if (alloc->last == block) {
and the code path you're referring to is only after this check fails,
i.e. it's no last entry, hence block->next can be never NULL.
So the current code is OK.
thanks,
Takashi
>
> To fix this possible bug, block->next is checked before using it.
>
> This bug is found by a static analysis tool STCheck written by us.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
> ---
> sound/isa/gus/gus_mem.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/sound/isa/gus/gus_mem.c b/sound/isa/gus/gus_mem.c
> index cb02d18dde60..ed6205b88057 100644
> --- a/sound/isa/gus/gus_mem.c
> +++ b/sound/isa/gus/gus_mem.c
> @@ -81,7 +81,8 @@ int snd_gf1_mem_xfree(struct snd_gf1_mem * alloc, struct snd_gf1_mem_block * blo
> if (block->prev)
> block->prev->next = NULL;
> } else {
> - block->next->prev = block->prev;
> + if (block->next)
> + block->next->prev = block->prev;
> if (block->prev)
> block->prev->next = block->next;
> }
> --
> 2.17.0
>
>
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