[PATCH v2] e100: prevent shift-out-of-bounds in e100_eeprom_load()

[pavankumaryalagada@gmail.com]

From: Yalagada Pavan Kumar <pavankumaryalagada@gmail.com>

When reading the EEPROM address length, e100_eeprom_read() can return
an invalid length (0 or >= 16). Passing an invalid addr_len to bit-shift
operations causes a shift out-of-bounds, triggering a kernel panic or
UBSAN warning.

Validate addr_len after reading it from EEPROM in both
e100_eeprom_load() and e100_eeprom_save(), and return -EIO if the value
is out of bounds.

Reported-by: syzbot+e0abb1d45ac291ebebeb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e0abb1d45ac291ebebeb
Signed-off-by: Yalagada Pavan Kumar <pavankumaryalagada@gmail.com>
---
Tested in QEMU using syzbot c reproducer.

v2:
- Return -EIO instead of -EINVAL for an invalid EEPROM address length.
- Validate addr_len in e100_eeprom_save() as well.
- Drop the unnecessary 1U change in the shift.
- Update the commit message.

v1:
https://lore.kernel.org/all/20260807145626.52692-1-pavankumaryalagada@gmail.com/T/
---
 drivers/net/ethernet/intel/e100.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/e100.c b/drivers/net/ethernet/intel/e100.c
index 1de5cd41ea0c..464dc2d6cdb5 100644
--- a/drivers/net/ethernet/intel/e100.c
+++ b/drivers/net/ethernet/intel/e100.c
@@ -775,10 +775,10 @@ static int e100_eeprom_load(struct nic *nic)
 		netif_err(nic, probe, nic->netdev,
 			"Invalid EEPROM address length %u\n",
 			addr_len);
-		return -EINVAL;
+		return -EIO;
 	}
 
-	nic->eeprom_wc = 1U << addr_len;
+	nic->eeprom_wc = 1 << addr_len;
 
 	for (addr = 0; addr < nic->eeprom_wc; addr++) {
 		nic->eeprom[addr] = e100_eeprom_read(nic, &addr_len, addr);
@@ -804,6 +804,14 @@ 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 >= 16) {
+		netif_err(nic, probe, nic->netdev,
+			"Invalid EEPROM address length %u\n",
+			addr_len);
+		return -EIO;
+	}
+
 	nic->eeprom_wc = 1 << addr_len;
 
 	if (start + count >= nic->eeprom_wc)
-- 
2.43.0