[PATCH net v1] wifi: p54: prevent buffer-overflow in p54_rx_eeprom_readback()

[Christian Lamparter <chunkeey@gmail.com>]

Robert Morris reported:

|If a malicious USB device pretends to be an Intersil p54 wifi
|interface and generates an eeprom_readback message with a large
|eeprom->v1.len, p54_rx_eeprom_readback() will copy data from the
|message beyond the end of priv->eeprom.
|
|static void p54_rx_eeprom_readback(struct p54_common *priv,
|                                   struct sk_buff *skb)
|{
|        struct p54_hdr *hdr = (struct p54_hdr *) skb->data;
|        struct p54_eeprom_lm86 *eeprom = (struct p54_eeprom_lm86 *) hdr->data;
|
|        if (priv->fw_var >= 0x509) {
|                memcpy(priv->eeprom, eeprom->v2.data,
|                       le16_to_cpu(eeprom->v2.len));
|        } else {
|                memcpy(priv->eeprom, eeprom->v1.data,
|                       le16_to_cpu(eeprom->v1.len));
|        }
| [...]

The eeprom->v{1,2}.len is set by the driver in p54_download_eeprom().
The device is supposed to provide the same length back to the driver.
But yes, it's possible (like shown in the report) to alter the value
to something that causes a crash/panic due to overrun.

This patch addresses the issue by adding the size to the common device
context, so p54_rx_eeprom_readback no longer relies on possibly tampered
values... That said, it also checks if the "firmware" altered the value
and no longer copies them.

The one, small saving grace is: Before the driver tries to read the eeprom,
it needs to upload >a< firmware. the vendor firmware has a proprietary
license and as a reason, it is not present on most distributions by
default.

Cc: <stable@kernel.org>
Reported-by: Robert Morris <rtm@mit.edu>
Closes: https://lore.kernel.org/linux-wireless/28782.1747258414@localhost/
Fixes: 7cb770729ba8 ("p54: move eeprom code into common library")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

---

First of all: Congratulation and Thank you! This is a great report.
the reprod. is the icing on the cake...
I guess you found more issues with p54, right?

From what I see, the first patch that introduced the "unchecked" buffer
overrun has a date of "Sep 1 22:48:51 2008 +0200"

I don't know who currently handles these patches, maybe netdev?
---
 drivers/net/wireless/intersil/p54/fwio.c |  2 ++
 drivers/net/wireless/intersil/p54/p54.h  |  1 +
 drivers/net/wireless/intersil/p54/txrx.c | 13 +++++++++----
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/intersil/p54/fwio.c b/drivers/net/wireless/intersil/p54/fwio.c
index 772084a9bd8d..3baf8ab01e22 100644
--- a/drivers/net/wireless/intersil/p54/fwio.c
+++ b/drivers/net/wireless/intersil/p54/fwio.c
@@ -231,6 +231,7 @@ int p54_download_eeprom(struct p54_common *priv, void *buf,
 
 	mutex_lock(&priv->eeprom_mutex);
 	priv->eeprom = buf;
+	priv->eeprom_slice_size = len;
 	eeprom_hdr = skb_put(skb, eeprom_hdr_size + len);
 
 	if (priv->fw_var < 0x509) {
@@ -253,6 +254,7 @@ int p54_download_eeprom(struct p54_common *priv, void *buf,
 		ret = -EBUSY;
 	}
 	priv->eeprom = NULL;
+	priv->eeprom_slice_size = 0;
 	mutex_unlock(&priv->eeprom_mutex);
 	return ret;
 }
diff --git a/drivers/net/wireless/intersil/p54/p54.h b/drivers/net/wireless/intersil/p54/p54.h
index 522656de4159..aeb5e40cc5ef 100644
--- a/drivers/net/wireless/intersil/p54/p54.h
+++ b/drivers/net/wireless/intersil/p54/p54.h
@@ -258,6 +258,7 @@ struct p54_common {
 
 	/* eeprom handling */
 	void *eeprom;
+	size_t eeprom_slice_size;
 	struct completion eeprom_comp;
 	struct mutex eeprom_mutex;
 };
diff --git a/drivers/net/wireless/intersil/p54/txrx.c b/drivers/net/wireless/intersil/p54/txrx.c
index 8414aa208655..2deb1bb54f24 100644
--- a/drivers/net/wireless/intersil/p54/txrx.c
+++ b/drivers/net/wireless/intersil/p54/txrx.c
@@ -496,14 +496,19 @@ static void p54_rx_eeprom_readback(struct p54_common *priv,
 		return ;
 
 	if (priv->fw_var >= 0x509) {
-		memcpy(priv->eeprom, eeprom->v2.data,
-		       le16_to_cpu(eeprom->v2.len));
+		if (le16_to_cpu(eeprom->v2.len) != priv->eeprom_slice_size)
+			return;
+
+		memcpy(priv->eeprom, eeprom->v2.data, priv->eeprom_slice_size);
 	} else {
-		memcpy(priv->eeprom, eeprom->v1.data,
-		       le16_to_cpu(eeprom->v1.len));
+		if (le16_to_cpu(eeprom->v1.len) != priv->eeprom_slice_size)
+			return;
+
+		memcpy(priv->eeprom, eeprom->v1.data, priv->eeprom_slice_size);
 	}
 
 	priv->eeprom = NULL;
+	priv->eeprom_slice_size = 0;
 	tmp = p54_find_and_unlink_skb(priv, hdr->req_id);
 	dev_kfree_skb_any(tmp);
 	complete(&priv->eeprom_comp);
-- 
2.49.0