[alsa-devel] [PATCH] ALSA: isa: gus: Fix a possible null-pointer dereference in snd_gf1_mem_xfree()
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.
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; }
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;-- 2.17.0
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;-- 2.17.0
participants (2)
-
Jia-Ju Bai -
Takashi Iwai