Subject: [PATCH 19/32] airo: Fix possible info leak in AIROOLDIOCTL/SIOCDEVPRIVATE

From: Michael Ellerman <[email-masked]>
Date: Wed, 22 Jan 2020 15:07:27 +1100

[ Upstream commit d6bce2137f5d6bb1093e96d2f801479099b28094 ]

The driver for Cisco Aironet 4500 and 4800 series cards (airo.c),
implements AIROOLDIOCTL/SIOCDEVPRIVATE in airo_ioctl().

The ioctl handler copies an aironet_ioctl struct from userspace, which
includes a command and a length. Some of the commands are handled in
readrids(), which kmalloc()'s a buffer of RIDSIZE (2048) bytes.

That buffer is then passed to PC4500_readrid(), which has two cases.
The else case does some setup and then reads up to RIDSIZE bytes from
the hardware into the kmalloc()'ed buffer.

Here len == RIDSIZE, pBuf is the kmalloc()'ed buffer:

	// read the rid length field
	bap_read(ai, pBuf, 2, BAP1);
	// length for remaining part of rid
	len = min(len, (int)le16_to_cpu(*(__le16*)pBuf)) - 2;
	...
	// read remainder of the rid
	rc = bap_read(ai, ((__le16*)pBuf)+1, len, BAP1);

PC4500_readrid() then returns to readrids() which does:

	len = comp->len;
	if (copy_to_user(comp->data, iobuf, min(len, (int)RIDSIZE))) {

Where comp->len is the user controlled length field.

So if the "rid length field" returned by the hardware is < 2048, and
the user requests 2048 bytes in comp->len, we will leak the previous
contents of the kmalloc()'ed buffer to userspace.

Fix it by kzalloc()'ing the buffer.

Found by Ilja by code inspection, not tested as I don't have the
required hardware.

Reported-by: Ilja Van Sprundel <[email-masked]>
Signed-off-by: Michael Ellerman <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 drivers/net/wireless/cisco/airo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/cisco/airo.c b/drivers/net/wireless/cisco/airo.c
index f43c06569ea1..d69c2ee7e206 100644
--- a/drivers/net/wireless/cisco/airo.c
+++ b/drivers/net/wireless/cisco/airo.c
@@ -7813,7 +7813,7 @@ static int readrids(struct net_device *dev, aironet_ioctl *comp) {
 		return -EINVAL;
 	}
 
-	if ((iobuf = kmalloc(RIDSIZE, GFP_KERNEL)) == NULL)
+	if ((iobuf = kzalloc(RIDSIZE, GFP_KERNEL)) == NULL)
 		return -ENOMEM;
 
 	PC4500_readrid(ai,ridcode,iobuf,RIDSIZE, 1);
-- 
2.21.1