[PATCH net] sfc: allocate a big enough SKB for loopback selftest packet

[PATCH net] sfc: allocate a big enough SKB for loopback selftest packet

[edward.cree]

From: Edward Cree <ecree.xilinx@gmail.com>

Cited commits passed a size to alloc_skb that was only big enough for
 the actual packet contents, but the following skb_put + memcpy writes
 the whole struct efx_loopback_payload including leading and trailing
 padding bytes (which are then stripped off with skb_pull/skb_trim).
This could cause an skb_over_panic, although in practice we get saved
 by kmalloc_size_roundup.
Pass the entire size we use, instead of the size of the final packet.

Reported-by: Andy Moreton <andy.moreton@amd.com>
Fixes: cf60ed469629 ("sfc: use padding to fix alignment in loopback test")
Fixes: 30c24dd87f3f ("sfc: siena: use padding to fix alignment in loopback test")
Fixes: 1186c6b31ee1 ("sfc: falcon: use padding to fix alignment in loopback test")
Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>
---
 drivers/net/ethernet/sfc/falcon/selftest.c | 2 +-
 drivers/net/ethernet/sfc/selftest.c        | 2 +-
 drivers/net/ethernet/sfc/siena/selftest.c  | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/sfc/falcon/selftest.c b/drivers/net/ethernet/sfc/falcon/selftest.c
index cf1d67b6d86d..c3dc88e6c26c 100644
--- a/drivers/net/ethernet/sfc/falcon/selftest.c
+++ b/drivers/net/ethernet/sfc/falcon/selftest.c
@@ -428,7 +428,7 @@ static int ef4_begin_loopback(struct ef4_tx_queue *tx_queue)
 	for (i = 0; i < state->packet_count; i++) {
 		/* Allocate an skb, holding an extra reference for
 		 * transmit completion counting */
-		skb = alloc_skb(EF4_LOOPBACK_PAYLOAD_LEN, GFP_KERNEL);
+		skb = alloc_skb(sizeof(state->payload), GFP_KERNEL);
 		if (!skb)
 			return -ENOMEM;
 		state->skbs[i] = skb;
diff --git a/drivers/net/ethernet/sfc/selftest.c b/drivers/net/ethernet/sfc/selftest.c
index 19a0b8584afb..563c1e317ce9 100644
--- a/drivers/net/ethernet/sfc/selftest.c
+++ b/drivers/net/ethernet/sfc/selftest.c
@@ -426,7 +426,7 @@ static int efx_begin_loopback(struct efx_tx_queue *tx_queue)
 	for (i = 0; i < state->packet_count; i++) {
 		/* Allocate an skb, holding an extra reference for
 		 * transmit completion counting */
-		skb = alloc_skb(EFX_LOOPBACK_PAYLOAD_LEN, GFP_KERNEL);
+		skb = alloc_skb(sizeof(state->payload), GFP_KERNEL);
 		if (!skb)
 			return -ENOMEM;
 		state->skbs[i] = skb;
diff --git a/drivers/net/ethernet/sfc/siena/selftest.c b/drivers/net/ethernet/sfc/siena/selftest.c
index b55fd3346972..526da43d4b61 100644
--- a/drivers/net/ethernet/sfc/siena/selftest.c
+++ b/drivers/net/ethernet/sfc/siena/selftest.c
@@ -426,7 +426,7 @@ static int efx_begin_loopback(struct efx_tx_queue *tx_queue)
 	for (i = 0; i < state->packet_count; i++) {
 		/* Allocate an skb, holding an extra reference for
 		 * transmit completion counting */
-		skb = alloc_skb(EFX_LOOPBACK_PAYLOAD_LEN, GFP_KERNEL);
+		skb = alloc_skb(sizeof(state->payload), GFP_KERNEL);
 		if (!skb)
 			return -ENOMEM;
 		state->skbs[i] = skb;

Re: [PATCH net] sfc: allocate a big enough SKB for loopback selftest packet

[Simon Horman]

On Mon, Aug 21, 2023 at 07:01:53PM +0100, edward.cree@amd.com wrote:
> From: Edward Cree <ecree.xilinx@gmail.com>
> 
> Cited commits passed a size to alloc_skb that was only big enough for
>  the actual packet contents, but the following skb_put + memcpy writes
>  the whole struct efx_loopback_payload including leading and trailing
>  padding bytes (which are then stripped off with skb_pull/skb_trim).
> This could cause an skb_over_panic, although in practice we get saved
>  by kmalloc_size_roundup.
> Pass the entire size we use, instead of the size of the final packet.
> 
> Reported-by: Andy Moreton <andy.moreton@amd.com>
> Fixes: cf60ed469629 ("sfc: use padding to fix alignment in loopback test")
> Fixes: 30c24dd87f3f ("sfc: siena: use padding to fix alignment in loopback test")
> Fixes: 1186c6b31ee1 ("sfc: falcon: use padding to fix alignment in loopback test")
> Signed-off-by: Edward Cree <ecree.xilinx@gmail.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH net] sfc: allocate a big enough SKB for loopback selftest packet

[patchwork-bot+netdevbpf]

Hello:

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

On Mon, 21 Aug 2023 19:01:53 +0100 you wrote:
> From: Edward Cree <ecree.xilinx@gmail.com>
> 
> Cited commits passed a size to alloc_skb that was only big enough for
>  the actual packet contents, but the following skb_put + memcpy writes
>  the whole struct efx_loopback_payload including leading and trailing
>  padding bytes (which are then stripped off with skb_pull/skb_trim).
> This could cause an skb_over_panic, although in practice we get saved
>  by kmalloc_size_roundup.
> Pass the entire size we use, instead of the size of the final packet.
> 
> [...]

Here is the summary with links:
  - [net] sfc: allocate a big enough SKB for loopback selftest packet
    https://git.kernel.org/netdev/net/c/6dc5774deefe

You are awesome, thank you!
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