Re: [PATCH v2] lib/firmware_table: validate subtable bounds

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 21 Oct 2026 23:01:59 +0800 Jiale Yao <yaojiale02@163.com> wrote:

> The generic firmware table walker dispatches matching entries after only
> checking that a generic subtable header is present. A record whose
> declared length is shorter than its header or extends past the table can
> therefore reach a handler before its bounds have been established.

Then what happens?  Kernel go oops?

When fixing a bug please always describe the userspace-visible runtime
effects of that bug.

How can this situation come about?  A messed up firmware table?

> Once a complete generic header is available, validate the declared record
> range before looking up or invoking a handler. This rejects zero-length
> and truncated records while preserving the existing behavior of ignoring
> trailing table data too short to contain another subtable header.
>
> ...
>
> --- a/lib/fw_table.c
> +++ b/lib/fw_table.c
> @@ -172,7 +172,15 @@ acpi_parse_entries_array(char *id, unsigned long table_size,
>  	    ((unsigned long)table_header + table_size);
>  	subtable_len = acpi_get_subtable_header_length(&entry);
>  
> -	while (((unsigned long)entry.hdr) + subtable_len < table_end) {
> +	while ((unsigned long)entry.hdr + subtable_len <= table_end) {
> +		entry_len = acpi_get_entry_length(&entry);
> +		if (entry_len < subtable_len ||
> +		    entry_len > table_end - (unsigned long)entry.hdr) {
> +			pr_err("[%4.4s:0x%02lx] Invalid length %lu\n", id,
> +			       acpi_get_entry_type(&entry), entry_len);
> +			return -EINVAL;
> +		}
> +
>  		for (i = 0; i < proc_num; i++) {
>  			if (acpi_get_entry_type(&entry) != proc[i].id)
>  				continue;
> @@ -186,16 +194,6 @@ acpi_parse_entries_array(char *id, unsigned long table_size,
>  			break;
>  		}
>  
> -		/*
> -		 * If entry->length is 0, break from this loop to avoid
> -		 * infinite loop.
> -		 */
> -		entry_len = acpi_get_entry_length(&entry);
> -		if (entry_len == 0) {
> -			pr_err("[%4.4s:0x%02x] Invalid zero length\n", id, proc->id);
> -			return -EINVAL;
> -		}
> -
>  		entry.hdr = (union acpi_subtable_headers *)
>  		    ((unsigned long)entry.hdr + entry_len);
>  	}
> -- 
> 2.34.1