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

[Malathi <malathi.a2000@gmail.com>]

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 same corrupted addr_len is also fed back into e100_eeprom_read() for
every subsequent word, where it is used as a shift count again:

	cmd_addr_data = ((op_read << *addr_len) | addr) << 16;

so validating the length only once at the caller is not enough.

Clamp the length in e100_eeprom_read() so the subtraction can never
underflow the u16, and reject a zero or out-of-range length in
e100_eeprom_load() and e100_eeprom_save() before using it. The EEPROM
cache holds at most 256 words, so a valid address length is in [1, 8].

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 <malathi.a2000@gmail.com>

diff --git a/drivers/net/ethernet/intel/e100.c b/drivers/net/ethernet/intel/e100.c
index 29960762e64a..26a7c0aaa6e2 100644
--- a/drivers/net/ethernet/intel/e100.c
+++ b/drivers/net/ethernet/intel/e100.c
@@ -744,7 +744,12 @@ static __le16 e100_eeprom_read(struct nic *nic, u16 *addr_len, u16 addr)
 		 * complete address.  Use this to adjust addr_len. */
 		ctrl = ioread8(&nic->csr->eeprom_ctrl_lo);
 		if (!(ctrl & eedo) && i > 16) {
-			*addr_len -= (i - 16);
+			u16 len = i - 16;
+
+			if (len > *addr_len)
+				*addr_len = 0;
+			else
+				*addr_len -= len;
 			i = 17;
 		}
 
@@ -765,6 +770,11 @@ 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 || 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 +801,11 @@ 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 || 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