[PATCH net 4/4] tg3: Fix heap overflow in unbuffered NVRAM write path

[Pavan Chebbi <pavan.chebbi@broadcom.com>]

From: Shravya KN <shravya.k-n@broadcom.com>

tg3_nvram_write_block_unbuffered() reads a whole NVRAM page into a
buffer of pagesize bytes, copies the caller's data into it at page_off,
and writes the page back.  The copy size was clamped to pagesize rather
than to the room left in the page, pagesize - page_off, so a write at an
offset that is not page aligned, as ETHTOOL_SEEPROM allows, copies past
the end of the buffer and corrupts the kernel heap.

Clamp size to pagesize - page_off.  Also advance buf by size on each
iteration, as the data of a write that spans pages was otherwise taken
from the start of the caller's buffer for every page.

This was found by an AI code review scan.  It has not been triggered, so
the issue is theoretical.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Vishvambar Panth S <vishvambar.panth-s@broadcom.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Shravya KN <shravya.k-n@broadcom.com>
Signed-off-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
---
 drivers/net/ethernet/broadcom/tg3.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index 16f8368874e7..5b5b21d759a6 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -3399,13 +3399,14 @@ static int tg3_nvram_write_block_unbuffered(struct tg3 *tp, u32 offset, u32 len,
 			break;
 
 		page_off = offset & pagemask;
-		size = pagesize;
+		size = pagesize - page_off;
 		if (len < size)
 			size = len;
 
 		len -= size;
 
 		memcpy(tmp + page_off, buf, size);
+		buf += size;
 
 		offset = offset + (pagesize - page_off);
 
-- 
2.52.0