Messages in this thread Patch in this message | | | Subject | Re: [PATCH] ALSA: isa: gus: Fix a possible null-pointer dereference in snd_gf1_mem_xfree() | From | Jia-Ju Bai <> | Date | Tue, 23 Jul 2019 21:51:28 +0800 |
| |
Thanks for the quick reply :) I think you are right, and I did not consider "if (alloc->last == block)" Sorry for the false report...
Best wishes, Jia-Ju Bai
On 2019/7/23 21:47, Takashi Iwai wrote: > 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@gmail.com> >> --- >> 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 >> >>
| |