[PATCH net v2] net: wwan: iosm: bound device offsets in the MUX downlink decoder

[Maoyi Xie <maoyixie.tju@gmail.com>]

mux_dl_adb_decode() walks a chain of aggregated datagram tables using
offsets and lengths taken from the modem. first_table_index,
next_table_index, table_length, datagram_index and datagram_length are
all device supplied le values. Only first_table_index was checked, and
only for being non zero. The decoder then formed adth = block +
adth_index and read the table header and the datagram entries with no
bound against the received skb. A modem that reports an index or a
length past the downlink buffer makes the decoder read out of bounds.

The buffer is IPC_MEM_MAX_DL_MUX_LITE_BUF_SIZE and skb->len is at most
that, so skb->len is the real limit, but none of these in band offsets
were checked against it.

Validate every device offset and length against skb->len before use.
The block header must fit. Each table header, on entry and after every
next_table_index, must lie inside the skb. The datagram table must fit.
Each datagram index and length must stay inside the skb. The header
padding must not exceed the datagram length so the receive length does
not wrap.

This was reproduced under KASAN as a slab out of bounds read on a normal
downlink receive once the iosm net device is up.

Fixes: 1f52d7b62285 ("net: wwan: iosm: Enable M.2 7360 WWAN card support")
Suggested-by: Loic Poulain <loic.poulain@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
---
Changes in v2:
- mux_dl_process_dg now uses intermediate native endian locals dg_index
  and dg_len so the bound checks read cleaner and avoid the repeated
  le32_to_cpu conversions, per Loic Poulain's review. No functional
  change.

Link to v1: https://lore.kernel.org/all/178185979029.4044562.9993615975949055530@maoyixie.com/

 drivers/net/wwan/iosm/iosm_ipc_mux_codec.c | 33 ++++++++++++++++------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wwan/iosm/iosm_ipc_mux_codec.c b/drivers/net/wwan/iosm/iosm_ipc_mux_codec.c
index bff46f7ca59f..ff9a4bc52f29 100644
--- a/drivers/net/wwan/iosm/iosm_ipc_mux_codec.c
+++ b/drivers/net/wwan/iosm/iosm_ipc_mux_codec.c
@@ -553,19 +553,21 @@ static int mux_dl_process_dg(struct iosm_mux *ipc_mux, struct mux_adbh *adbh,
 	u32 packet_offset, i, rc, dg_len;
 
 	for (i = 0; i < nr_of_dg; i++, dg++) {
-		if (le32_to_cpu(dg->datagram_index)
-				< sizeof(struct mux_adbh))
+		u32 dg_index = le32_to_cpu(dg->datagram_index);
+
+		dg_len = le16_to_cpu(dg->datagram_length);
+
+		if (dg_index < sizeof(struct mux_adbh))
 			goto dg_error;
 
-		/* Is the packet inside of the ADB */
-		if (le32_to_cpu(dg->datagram_index) >=
-					le32_to_cpu(adbh->block_length)) {
+		/* Is the packet inside of the ADB and the received skb ? */
+		if (dg_index >= le32_to_cpu(adbh->block_length) ||
+		    dg_index >= skb->len ||
+		    dg_len > skb->len - dg_index ||
+		    dl_head_pad_len >= dg_len) {
 			goto dg_error;
 		} else {
-			packet_offset =
-				le32_to_cpu(dg->datagram_index) +
-				dl_head_pad_len;
-			dg_len = le16_to_cpu(dg->datagram_length);
+			packet_offset = dg_index + dl_head_pad_len;
 			/* Pass the packet to the netif layer. */
 			rc = ipc_mux_net_receive(ipc_mux, if_id, ipc_mux->wwan,
 						 packet_offset,
@@ -595,6 +597,10 @@ static void mux_dl_adb_decode(struct iosm_mux *ipc_mux,
 	block = skb->data;
 	adbh = (struct mux_adbh *)block;
 
+	/* The block header itself must fit in the received skb. */
+	if (skb->len < sizeof(struct mux_adbh))
+		goto adb_decode_err;
+
 	/* Process the aggregated datagram tables. */
 	adth_index = le32_to_cpu(adbh->first_table_index);
 
@@ -606,6 +612,11 @@ static void mux_dl_adb_decode(struct iosm_mux *ipc_mux,
 
 	/* Loop through mixed session tables. */
 	while (adth_index) {
+		/* The table header must lie within the received skb. */
+		if (adth_index < sizeof(struct mux_adbh) ||
+		    adth_index > skb->len - sizeof(struct mux_adth))
+			goto adb_decode_err;
+
 		/* Get the reference to the table header. */
 		adth = (struct mux_adth *)(block + adth_index);
 
@@ -629,6 +640,10 @@ static void mux_dl_adb_decode(struct iosm_mux *ipc_mux,
 		if (le16_to_cpu(adth->table_length) < sizeof(struct mux_adth))
 			goto adb_decode_err;
 
+		/* The whole datagram table must fit in the received skb. */
+		if (le16_to_cpu(adth->table_length) > skb->len - adth_index)
+			goto adb_decode_err;
+
 		/* Calculate the number of datagrams. */
 		nr_of_dg = (le16_to_cpu(adth->table_length) -
 					sizeof(struct mux_adth)) /
-- 
2.34.1