[net,1/4] can: j1939: j1939_tp_tx_dat_new(): fix out-of-bounds memory access

Commit Message

Marc Kleine-Budde April 5, 2023, 9:24 a.m. UTC

From: Oleksij Rempel <[e-mail]>

In the j1939_tp_tx_dat_new() function, an out-of-bounds memory access
could occur during the memcpy() operation if the size of skb->cb is
larger than the size of struct j1939_sk_buff_cb. This is because the
memcpy() operation uses the size of skb->cb, leading to a read beyond
the struct j1939_sk_buff_cb.

Updated the memcpy() operation to use the size of struct
j1939_sk_buff_cb instead of the size of skb->cb. This ensures that the
memcpy() operation only reads the memory within the bounds of struct
j1939_sk_buff_cb, preventing out-of-bounds memory access.

Additionally, add a BUILD_BUG_ON() to check that the size of skb->cb
is greater than or equal to the size of struct j1939_sk_buff_cb. This
ensures that the skb->cb buffer is large enough to hold the
j1939_sk_buff_cb structure.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Reported-by: Shuangpeng Bai <[e-mail]>
Tested-by: Shuangpeng Bai <[e-mail]>
Signed-off-by: Oleksij Rempel <[e-mail]>
Link: https://groups.google.com/g/syzkaller/c/G_LL-C3plRs/m/-8xCi6dCAgAJ
Link: https://lore.kernel.org/all/[e-mail]
Cc: [e-mail]
[mkl: rephrase commit message]
Signed-off-by: Marc Kleine-Budde <[e-mail]>
---
 net/can/j1939/transport.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)


base-commit: 3ce9345580974863c060fa32971537996a7b2d57

Comments

[e-mail] April 6, 2023, 12:30 a.m. UTC | #1

Hello:

This series was applied to netdev/net.git (main)
by Marc Kleine-Budde <[e-mail]>:

On Wed,  5 Apr 2023 11:24:41 +0200 you wrote:
> From: Oleksij Rempel <[e-mail]>
> 
> In the j1939_tp_tx_dat_new() function, an out-of-bounds memory access
> could occur during the memcpy() operation if the size of skb->cb is
> larger than the size of struct j1939_sk_buff_cb. This is because the
> memcpy() operation uses the size of skb->cb, leading to a read beyond
> the struct j1939_sk_buff_cb.
> 
> [...]

Here is the summary with links:
  - [net,1/4] can: j1939: j1939_tp_tx_dat_new(): fix out-of-bounds memory access
    https://git.kernel.org/netdev/net/c/b45193cb4df5
  - [net,2/4] can: isotp: isotp_recvmsg(): use sock_recv_cmsgs() to get SOCK_RXQ_OVFL infos
    https://git.kernel.org/netdev/net/c/0145462fc802
  - [net,3/4] can: isotp: isotp_ops: fix poll() to not report false EPOLLOUT events
    https://git.kernel.org/netdev/net/c/79e19fa79cb5
  - [net,4/4] can: isotp: fix race between isotp_sendsmg() and isotp_release()
    https://git.kernel.org/netdev/net/c/051737439eae

You are awesome, thank you!

Patch

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index fb92c3609e17..fe3df23a2595 100644
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -604,7 +604,10 @@  sk_buff *j1939_tp_tx_dat_new(struct j1939_priv *priv,
 	/* reserve CAN header */
 	skb_reserve(skb, offsetof(struct can_frame, data));
 
-	memcpy(skb->cb, re_skcb, sizeof(skb->cb));
+	/* skb->cb must be large enough to hold a j1939_sk_buff_cb structure */
+	BUILD_BUG_ON(sizeof(skb->cb) < sizeof(*re_skcb));
+
+	memcpy(skb->cb, re_skcb, sizeof(*re_skcb));
 	skcb = j1939_skb_to_cb(skb);
 	if (swap_src_dst)
 		j1939_skbcb_swap(skcb);