[PATCH net] e100: fix shift-out-of-bounds in e100_eeprom_load()

e100_eeprom_load() and e100_eeprom_save() start with an address length
of 8 and call e100_eeprom_read() to auto-detect the real EEPROM address
length. e100_eeprom_read() adjusts the length with

	*addr_len -= (i - 16);

based on when the EEPROM drives a dummy zero onto EEDO. A malfunctioning
or emulated device that drives EEDO low too early makes (i - 16) exceed
the current length, underflowing the u16 addr_len to a large value such
as 65529.

That value is then used as a shift count:

	nic->eeprom_wc = 1 << addr_len;

which is undefined behaviour and additionally overflows the fixed-size
nic->eeprom[256] cache.

  UBSAN: shift-out-of-bounds in drivers/net/ethernet/intel/e100.c:768:21
  shift exponent 65529 is too large for 32-bit type 'int'

The EEPROM cache holds at most 256 words, so a valid address length is
never larger than 8. Reject larger values before using addr_len.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+e0abb1d45ac291ebebeb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e0abb1d45ac291ebebeb
Signed-off-by: Malathi <redacted>
---
 drivers/net/ethernet/intel/e100.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/ethernet/intel/e100.c b/drivers/net/ethernet/intel/e100.c
index 29960762e64a..a236273f5e65 100644
--- a/drivers/net/ethernet/intel/e100.c
+++ b/drivers/net/ethernet/intel/e100.c

@@ -765,6 +765,11 @@ static int e100_eeprom_load(struct nic *nic)
 
 	/* Try reading with an 8-bit addr len to discover actual addr len */
 	e100_eeprom_read(nic, &addr_len, 0);
+	if (addr_len > 8) {
+		netif_err(nic, probe, nic->netdev,
+			  "invalid EEPROM address length %u\n", addr_len);
+		return -EINVAL;
+	}
 	nic->eeprom_wc = 1 << addr_len;
 
 	for (addr = 0; addr < nic->eeprom_wc; addr++) {

@@ -791,6 +796,11 @@ static int e100_eeprom_save(struct nic *nic, u16 start, u16 count)
 
 	/* Try reading with an 8-bit addr len to discover actual addr len */
 	e100_eeprom_read(nic, &addr_len, 0);
+	if (addr_len > 8) {
+		netif_err(nic, probe, nic->netdev,
+			  "invalid EEPROM address length %u\n", addr_len);
+		return -EINVAL;
+	}
 	nic->eeprom_wc = 1 << addr_len;
 
 	if (start + count >= nic->eeprom_wc)

-- 
2.43.0