[PATCH net v2] mac802154: llsec: reject frames shorter than the authentication tag

[PATCH net v2] mac802154: llsec: reject frames shorter than the authentication tag

[Doruk Tan Ozturk]

llsec_do_decrypt_auth() computes the associated-data length for the
AEAD request as

	assoclen += datalen - authlen;

where datalen is the number of bytes after the MAC header and authlen
(4, 8 or 16) is the length of the authentication tag. Nothing verifies
that the frame actually carries at least authlen payload bytes. A
secured frame whose payload is shorter than the tag makes
datalen - authlen negative; assoclen is then passed to
aead_request_set_ad() as an unsigned value close to 4 GiB, so
crypto_aead_decrypt() walks far off the end of the scatterlist that
only spans the real frame.

The frame is fully attacker-controlled and reaches this path from any
IEEE 802.15.4 peer in radio range. Reject frames whose payload is
shorter than the authentication tag before the subtraction.

Dynamically reproduced on a KASAN kernel as a general-protection-fault
in the AEAD scatterwalk, and the fix confirmed.

Fixes: 4c14a2fb5d14 ("mac802154: add llsec decryption method")
Cc: stable@vger.kernel.org
Assisted-by: 0sec:multi-model
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---

v2 (Breno Leitao review):
 - drop the redundant self-Reported-by.
 - move the length check above sg_init_one() (datalen/authlen are
   already available there).
 - Assisted-by trailer -> 0sec:multi-model.
Carrying Simon Horman Reviewed-by; v2 only moves the same check earlier.
 net/mac802154/llsec.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/mac802154/llsec.c b/net/mac802154/llsec.c
index 5e7cc11fab3a..85452ef9a58c 100644
--- a/net/mac802154/llsec.c
+++ b/net/mac802154/llsec.c
@@ -891,6 +891,11 @@ llsec_do_decrypt_auth(struct sk_buff *skb, const struct mac802154_llsec *sec,
 	data = skb_mac_header(skb) + skb->mac_len;
 	datalen = skb_tail_pointer(skb) - data;
 
+	if (datalen < authlen) {
+		kfree_sensitive(req);
+		return -EBADMSG;
+	}
+
 	sg_init_one(&sg, skb_mac_header(skb), assoclen + datalen);
 
 	if (!(hdr->sec.level & IEEE802154_SCF_SECLEVEL_ENC)) {
-- 
2.43.0

[PATCH net v2] mac802154: llsec: reject frames shorter than the authentication tag

[Doruk Tan Ozturk]

llsec_do_decrypt_auth() computes the associated-data length for the
AEAD request as

	assoclen += datalen - authlen;

where datalen is the number of bytes after the MAC header and authlen
(4, 8 or 16) is the length of the authentication tag. Nothing verifies
that the frame actually carries at least authlen payload bytes. A
secured frame whose payload is shorter than the tag makes
datalen - authlen negative; assoclen is then passed to
aead_request_set_ad() as an unsigned value close to 4 GiB, so
crypto_aead_decrypt() walks far off the end of the scatterlist that
only spans the real frame.

The frame is fully attacker-controlled and reaches this path from any
IEEE 802.15.4 peer in radio range. Reject frames whose payload is
shorter than the authentication tag before the subtraction.

Dynamically reproduced on a KASAN kernel as a general-protection-fault
in the AEAD scatterwalk, and the fix confirmed.

Fixes: 4c14a2fb5d14 ("mac802154: add llsec decryption method")
Cc: stable@vger.kernel.org
Assisted-by: 0sec:multi-model
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
---

v2 (Breno Leitao review):
 - drop the redundant self-Reported-by.
 - move the length check above sg_init_one() (datalen/authlen are
   already available there).
 - Assisted-by trailer -> 0sec:multi-model.
Carrying Simon Horman Reviewed-by; v2 only moves the same check earlier.
 net/mac802154/llsec.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/mac802154/llsec.c b/net/mac802154/llsec.c
index 5e7cc11fab3a..85452ef9a58c 100644
--- a/net/mac802154/llsec.c
+++ b/net/mac802154/llsec.c
@@ -891,6 +891,11 @@ llsec_do_decrypt_auth(struct sk_buff *skb, const struct mac802154_llsec *sec,
 	data = skb_mac_header(skb) + skb->mac_len;
 	datalen = skb_tail_pointer(skb) - data;
 
+	if (datalen < authlen) {
+		kfree_sensitive(req);
+		return -EBADMSG;
+	}
+
 	sg_init_one(&sg, skb_mac_header(skb), assoclen + datalen);
 
 	if (!(hdr->sec.level & IEEE802154_SCF_SECLEVEL_ENC)) {
-- 
2.43.0

Re: [PATCH net v2] mac802154: llsec: reject frames shorter than the authentication tag

[Breno Leitao]

On Thu, Jul 16, 2026 at 09:31:06PM +0200, Doruk Tan Ozturk wrote:
> llsec_do_decrypt_auth() computes the associated-data length for the
> AEAD request as
> 
> 	assoclen += datalen - authlen;
> 
> where datalen is the number of bytes after the MAC header and authlen
> (4, 8 or 16) is the length of the authentication tag. Nothing verifies
> that the frame actually carries at least authlen payload bytes. A
> secured frame whose payload is shorter than the tag makes
> datalen - authlen negative; assoclen is then passed to
> aead_request_set_ad() as an unsigned value close to 4 GiB, so
> crypto_aead_decrypt() walks far off the end of the scatterlist that
> only spans the real frame.
> 
> The frame is fully attacker-controlled and reaches this path from any
> IEEE 802.15.4 peer in radio range. Reject frames whose payload is
> shorter than the authentication tag before the subtraction.
> 
> Dynamically reproduced on a KASAN kernel as a general-protection-fault
> in the AEAD scatterwalk, and the fix confirmed.
> 
> Fixes: 4c14a2fb5d14 ("mac802154: add llsec decryption method")
> Cc: stable@vger.kernel.org
> Assisted-by: 0sec:multi-model
> Reviewed-by: Simon Horman <horms@kernel.org>
> Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>

Reviwed-by: Breno Leitao <leitao@debian.org>

Re: [PATCH net v2] mac802154: llsec: reject frames shorter than the authentication tag

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 16 Jul 2026 21:34:23 +0200 you wrote:
> llsec_do_decrypt_auth() computes the associated-data length for the
> AEAD request as
> 
> 	assoclen += datalen - authlen;
> 
> where datalen is the number of bytes after the MAC header and authlen
> (4, 8 or 16) is the length of the authentication tag. Nothing verifies
> that the frame actually carries at least authlen payload bytes. A
> secured frame whose payload is shorter than the tag makes
> datalen - authlen negative; assoclen is then passed to
> aead_request_set_ad() as an unsigned value close to 4 GiB, so
> crypto_aead_decrypt() walks far off the end of the scatterlist that
> only spans the real frame.
> 
> [...]

Here is the summary with links:
  - [net,v2] mac802154: llsec: reject frames shorter than the authentication tag
    https://git.kernel.org/netdev/net/c/fd3a3f28ed60

You are awesome, thank you!
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