[PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Norbert van Bolhuis]

This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
are sent from the pkt queue.

The problem is the number of entries in the pre-allocated sgtable, it is
nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
Given the default [rt]xglom_size=32 it's actually 35 which is too small.
Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
is added for each original SKB if tailroom isn't enough to hold tail_pad.
At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
NULL and this causes the oops.

The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
the worst-case.
Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
additional bytes of memory.
---
 drivers/net/wireless/broadcom/brcm80211/brcmfmac/bcmsdh.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/bcmsdh.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/bcmsdh.c
index 17f6b33beabd..42d991d9f8cb 100644
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/bcmsdh.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/bcmsdh.c
@@ -770,7 +770,7 @@ void brcmf_sdiod_sgtable_alloc(struct brcmf_sdio_dev *sdiodev)
 
 	nents = max_t(uint, BRCMF_DEFAULT_RXGLOM_SIZE,
 		      sdiodev->settings->bus.sdio.txglomsz);
-	nents += (nents >> 4) + 1;
+	nents *= 2;
 
 	WARN_ON(nents > sdiodev->max_segment_count);
 
-- 
2.42.0

Re: [PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Kalle Valo]

Norbert van Bolhuis <nvbolhuis@gmail.com> writes:

> This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
> when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
> are sent from the pkt queue.
>
> The problem is the number of entries in the pre-allocated sgtable, it is
> nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
> Given the default [rt]xglom_size=32 it's actually 35 which is too small.
> Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
> is added for each original SKB if tailroom isn't enough to hold tail_pad.
> At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
> in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
> NULL and this causes the oops.

BTW it would be good to fix (in a separate patch) the sg handling so
that the kernel won't oops when sg entries rung. That's not really
robust behaviour.

> The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
> the worst-case.
> Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
> additional bytes of memory.

s-o-b missing, please read our documentation from the link below.

-- 
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

Re: [PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Arend van Spriel]

On 11/7/2024 9:07 AM, Kalle Valo wrote:
> Norbert van Bolhuis <nvbolhuis@gmail.com> writes:
> 
>> This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
>> when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
>> are sent from the pkt queue.
>>
>> The problem is the number of entries in the pre-allocated sgtable, it is
>> nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
>> Given the default [rt]xglom_size=32 it's actually 35 which is too small.
>> Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
>> is added for each original SKB if tailroom isn't enough to hold tail_pad.
>> At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
>> in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
>> NULL and this causes the oops.
> 
> BTW it would be good to fix (in a separate patch) the sg handling so
> that the kernel won't oops when sg entries rung. That's not really
> robust behaviour.
> 
>> The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
>> the worst-case.
>> Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
>> additional bytes of memory.
> 
> s-o-b missing, please read our documentation from the link below.

I have not seen the actual patch. Which mailing list was it sent to?

Regards,
Arend

Re: [PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Kalle Valo]

Arend van Spriel <arend.vanspriel@broadcom.com> writes:

> On 11/7/2024 9:07 AM, Kalle Valo wrote:
>
>> Norbert van Bolhuis <nvbolhuis@gmail.com> writes:
>> 
>>> This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
>>> when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
>>> are sent from the pkt queue.
>>>
>>> The problem is the number of entries in the pre-allocated sgtable, it is
>>> nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
>>> Given the default [rt]xglom_size=32 it's actually 35 which is too small.
>>> Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
>>> is added for each original SKB if tailroom isn't enough to hold tail_pad.
>>> At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
>>> in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
>>> NULL and this causes the oops.
>> BTW it would be good to fix (in a separate patch) the sg handling so
>> that the kernel won't oops when sg entries rung. That's not really
>> robust behaviour.
>> 
>>> The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
>>> the worst-case.
>>> Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
>>> additional bytes of memory.
>> s-o-b missing, please read our documentation from the link below.
>
> I have not seen the actual patch. Which mailing list was it sent to?

Only to linux-wireless, adding brcm80211 now. But the patch is in
patchwork:

https://patchwork.kernel.org/project/linux-wireless/patch/20241105204011.1603148-1-norbert.vanbolhuis@ev-box.com/

-- 
https://patchwork.kernel.org/project/linux-wireless/list/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches

Re: [PATCH] wifi: brcmfmac: Fix oops due to NULL pointer dereference in 'brcmf_sdiod_sglist_rw'

[Arend van Spriel]

On 11/7/2024 10:51 AM, Kalle Valo wrote:
> Arend van Spriel <arend.vanspriel@broadcom.com> writes:
> 
>> On 11/7/2024 9:07 AM, Kalle Valo wrote:
>>
>>> Norbert van Bolhuis <nvbolhuis@gmail.com> writes:
>>>
>>>> This patch fixes a NULL pointer dereference bug in brcmfmac that occurs
>>>> when a high 'sd_sgentry_align' value applies (e.g. 512) and a lot of queued SKBs
>>>> are sent from the pkt queue.
>>>>
>>>> The problem is the number of entries in the pre-allocated sgtable, it is
>>>> nents = max(rxglom_size, txglom_size) + max(rxglom_size, txglom_size) >> 4 + 1.
>>>> Given the default [rt]xglom_size=32 it's actually 35 which is too small.
>>>> Worst case, the pkt queue can end up with 64 SKBs. This occurs when a new SKB
>>>> is added for each original SKB if tailroom isn't enough to hold tail_pad.
>>>> At least one sg entry is needed for each SKB. So, eventually the "skb_queue_walk loop"
>>>> in brcmf_sdiod_sglist_rw may run out of sg entries. This makes sg_next return
>>>> NULL and this causes the oops.
>>> BTW it would be good to fix (in a separate patch) the sg handling so
>>> that the kernel won't oops when sg entries rung. That's not really
>>> robust behaviour.
>>>
>>>> The patch sets nents to max(rxglom_size, txglom_size) * 2 to be able handle
>>>> the worst-case.
>>>> Btw. this requires only 64-35=29 * 16 (or 20 if CONFIG_NEED_SG_DMA_LENGTH) = 464
>>>> additional bytes of memory.
>>> s-o-b missing, please read our documentation from the link below.
>>
>> I have not seen the actual patch. Which mailing list was it sent to?
> 
> Only to linux-wireless, adding brcm80211 now. But the patch is in
> patchwork:
> 
> https://patchwork.kernel.org/project/linux-wireless/patch/20241105204011.1603148-1-norbert.vanbolhuis@ev-box.com/

Thanks, Kalle

I am also subscribed to linux-wireless, but search in thunderbird client 
did not come up with it. Thanks for the patchwork link. I should have 
checked that first.

Gr. AvS