RE: [Intel-wired-lan] [PATCH net-next v2] e100: fix shift-out-of-bounds in e100_eeprom_load()

[Loktionov, Aleksandr]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@xxxxxxxxxx> On Behalf
> Of Malathi
> Sent: Tuesday, August 11, 2026 7:08 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@xxxxxxxxx>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@xxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; intel-wired-lan@xxxxxxxxxxxxxxxx;
> kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; edumazet@xxxxxxxxxx;
> andrew+netdev@xxxxxxx; davem@xxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Malathi <malathi.a2000@xxxxxxxxx>;
> syzbot+e0abb1d45ac291ebebeb@xxxxxxxxxxxxxxxxxxxxxxxxx
> Subject: [Intel-wired-lan] [PATCH net-next v2] 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 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].
> 
> Reported-by: syzbot+e0abb1d45ac291ebebeb@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=e0abb1d45ac291ebebeb
> Signed-off-by: Malathi <malathi.a2000@xxxxxxxxx>
> ---
> v2:
>  - Drop the Fixes: tag and retarget to net-next; the underflow is only
>    reachable with malfunctioning or emulated hardware, so this is a
>    hardening change and not stable material.
>  - Clamp addr_len inside e100_eeprom_read() so the auto-detect
>    subtraction can never underflow the u16.  The corrupted length was
>    otherwise reused as a shift count for every subsequent word, so
>    validating it only once at the callers (as in v1) was not enough.
>  - Also reject a zero address length in e100_eeprom_load() and
>    e100_eeprom_save().
> 
>  drivers/net/ethernet/intel/e100.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> 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

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@xxxxxxxxx>