[Precise Quantal CVE-2013-1929] tg3: fix length overflow in VPD firmware parsing

[Luis Henriques]

From: Kees Cook <keescook at chromium.org>

CVE-2013-1929

BugLink: http://bugs.launchpad.net/bugs/1167065

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 at chromium.org>
Reported-by: Oded Horovitz <oded at privatecore.com>
Reported-by: Brad Spengler <spender at grsecurity.net>
Cc: stable at vger.kernel.org
Cc: Matt Carlson <mcarlson at broadcom.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 715230a44310a8cf66fbfb5a46f9a62a9b2de424)

Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/net/ethernet/broadcom/tg3.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index ca3be73..c2450f4 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -13617,8 +13617,11 @@ static void __devinit tg3_read_vpd(struct tg3 *tp)
 		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:
-- 
1.8.1.2