[36/74] tg3: fix length overflow in VPD firmware parsing

[Ben Hutchings <ben@decadent.org.uk>]

3.2.43-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

commit 715230a44310a8cf66fbfb5a46f9a62a9b2de424 upstream.

Commit 184b89044fb6e2a74611dafa69b1dce0d98612c6 ("tg3: Use VPD fw version
when present") introduced VPD parsing that contained a potential length
overflow.

Limit the hardware's reported firmware string length (max 255 bytes) to
stay inside the driver's firmware string length (32 bytes). On overflow,
truncate the formatted firmware string instead of potentially overwriting
portions of the tg3 struct.

http://cansecwest.com/slides/2013/PrivateCore%20CSW%202013.pdf

Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Oded Horovitz <oded@privatecore.com>
Reported-by: Brad Spengler <spender@grsecurity.net>
Cc: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/net/ethernet/broadcom/tg3.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -13433,8 +13433,11 @@ static void __devinit tg3_read_vpd(struc
 		if (j + len > block_end)
 			goto partno;
 
-		memcpy(tp->fw_ver, &vpd_data[j], len);
-		strncat(tp->fw_ver, " bc ", vpdlen - len - 1);
+		if (len >= sizeof(tp->fw_ver))
+			len = sizeof(tp->fw_ver) - 1;
+		memset(tp->fw_ver, 0, sizeof(tp->fw_ver));
+		snprintf(tp->fw_ver, sizeof(tp->fw_ver), "%.*s bc ", len,
+			 &vpd_data[j]);
 	}
 
 partno: