[PATCH v3] net/sched: em_canid: fix uninit-value in em_canid_match

[PATCH v3] net/sched: em_canid: fix uninit-value in em_canid_match

[ssrane_b23]

From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

Use pskb_may_pull() to ensure a complete CAN frame is present in the
linear data buffer before reading the CAN ID. A simple skb->len check
is insufficient because it only verifies the total data length but does
not guarantee the data is present in skb->data (it could be in
fragments).

pskb_may_pull() both validates the length and pulls fragmented data
into the linear buffer if necessary, making it safe to directly
access skb->data.

Reported-by: syzbot+5d8269a1e099279152bc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5d8269a1e099279152bc
Fixes: f057bbb6f9ed ("net: em_canid: Ematch rule to match CAN frames according to their identifiers")
Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
v3: Use CAN_MTU to validate a complete CAN frame is present
v2: Use pskb_may_pull() instead of skb->len check to properly
    handle fragmented skbs
---
 net/sched/em_canid.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/em_canid.c b/net/sched/em_canid.c
index 5337bc462755..2d27f91d8441 100644
--- a/net/sched/em_canid.c
+++ b/net/sched/em_canid.c
@@ -99,6 +99,9 @@ static int em_canid_match(struct sk_buff *skb, struct tcf_ematch *m,
 	int i;
 	const struct can_filter *lp;
 
+	if (!pskb_may_pull(skb, CAN_MTU))
+		return 0;
+
 	can_id = em_canid_get_id(skb);
 
 	if (can_id & CAN_EFF_FLAG) {
-- 
2.34.1

Re: [PATCH v3] net/sched: em_canid: fix uninit-value in em_canid_match

[Eric Dumazet]

On Wed, Nov 26, 2025 at 12:57 AM <ssrane_b23@ee.vjti.ac.in> wrote:
>
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
>
> Use pskb_may_pull() to ensure a complete CAN frame is present in the
> linear data buffer before reading the CAN ID. A simple skb->len check
> is insufficient because it only verifies the total data length but does
> not guarantee the data is present in skb->data (it could be in
> fragments).
>
> pskb_may_pull() both validates the length and pulls fragmented data
> into the linear buffer if necessary, making it safe to directly
> access skb->data.
>
> Reported-by: syzbot+5d8269a1e099279152bc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5d8269a1e099279152bc
> Fixes: f057bbb6f9ed ("net: em_canid: Ematch rule to match CAN frames according to their identifiers")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> ---
> v3: Use CAN_MTU to validate a complete CAN frame is present
> v2: Use pskb_may_pull() instead of skb->len check to properly
>     handle fragmented skbs
> ---
>  net/sched/em_canid.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/net/sched/em_canid.c b/net/sched/em_canid.c
> index 5337bc462755..2d27f91d8441 100644
> --- a/net/sched/em_canid.c
> +++ b/net/sched/em_canid.c
> @@ -99,6 +99,9 @@ static int em_canid_match(struct sk_buff *skb, struct tcf_ematch *m,
>         int i;
>         const struct can_filter *lp;
>
> +       if (!pskb_may_pull(skb, CAN_MTU))
> +               return 0;
> +
>         can_id = em_canid_get_id(skb);
>
>         if (can_id & CAN_EFF_FLAG) {

For your next netdev patches, please read
Documentation/process/maintainer-netdev.rst

Resending after review
~~~~~~~~~~~~~~~~~~~~~~

Allow at least 24 hours to pass between postings. This will ensure reviewers
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too long (weeks) between postings either as it will make it harder for reviewers
to recall all the context.

Thank you.

Re: [PATCH v3] net/sched: em_canid: fix uninit-value in em_canid_match

[Marc Kleine-Budde]

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On 26.11.2025 14:27:18, ssrane_b23@ee.vjti.ac.in wrote:
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
>
> Use pskb_may_pull() to ensure a complete CAN frame is present in the
> linear data buffer before reading the CAN ID. A simple skb->len check
> is insufficient because it only verifies the total data length but does
> not guarantee the data is present in skb->data (it could be in
> fragments).
>
> pskb_may_pull() both validates the length and pulls fragmented data
> into the linear buffer if necessary, making it safe to directly
> access skb->data.
>
> Reported-by: syzbot+5d8269a1e099279152bc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5d8269a1e099279152bc
> Fixes: f057bbb6f9ed ("net: em_canid: Ematch rule to match CAN frames according to their identifiers")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>

Applied to linux-can

regards,
Marc

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