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Commit bfbaafae authored by Jean Delvare's avatar Jean Delvare Committed by Matt Fleming
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firmware: dmi_scan: Prevent dmi_num integer overflow 



dmi_num is a u16, dmi_len is a u32, so this construct:

	dmi_num = dmi_len / 4;

would result in an integer overflow for a DMI table larger than
256 kB. I've never see such a large table so far, but SMBIOS 3.0
makes it possible so maybe we'll see such tables in the future.

So instead of faking a structure count when the entry point does
not provide it, adjust the loop condition in dmi_table() to properly
deal with the case where dmi_num is not set.

This bug was introduced with the initial SMBIOS 3.0 support in commit
fc430262 ("dmi: add support for SMBIOS 3.0 64-bit entry point").

Signed-off-by: default avatarJean Delvare <jdelvare@suse.de>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Cc: <stable@vger.kernel.org>
Acked-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarMatt Fleming <matt.fleming@intel.com>
parent 6d9ff473

drivers/firmware/dmi_scan.c

+7 −15
Original line number Diff line number Diff line
@@ -86,10 +86,13 @@ static void dmi_table(u8 *buf, u32 len, int num, 
	int i = 0;



	/*

	 *	Stop when we see all the items the table claimed to have

	 *	OR we run off the end of the table (also happens)

	 * Stop when we have seen all the items the table claimed to have

	 * (SMBIOS < 3.0 only) OR we reach an end-of-table marker OR we run

	 * off the end of the table (should never happen but sometimes does

	 * on bogus implementations.)

	 */

	while ((i < num) && (data - buf + sizeof(struct dmi_header)) <= len) {

	while ((!num || i < num) &&

	       (data - buf + sizeof(struct dmi_header)) <= len) {

		const struct dmi_header *dm = (const struct dmi_header *)data;



		/*
@@ -529,21 +532,10 @@ static int __init dmi_smbios3_present(const u8 *buf) 
	if (memcmp(buf, "_SM3_", 5) == 0 &&

	    buf[6] < 32 && dmi_checksum(buf, buf[6])) {

		dmi_ver = get_unaligned_be16(buf + 7);

		dmi_num = 0;			/* No longer specified */

		dmi_len = get_unaligned_le32(buf + 12);

		dmi_base = get_unaligned_le64(buf + 16);



		/*

		 * The 64-bit SMBIOS 3.0 entry point no longer has a field

		 * containing the number of structures present in the table.

		 * Instead, it defines the table size as a maximum size, and

		 * relies on the end-of-table structure type (#127) to be used

		 * to signal the end of the table.

		 * So let's define dmi_num as an upper bound as well: each

		 * structure has a 4 byte header, so dmi_len / 4 is an upper

		 * bound for the number of structures in the table.

		 */

		dmi_num = dmi_len / 4;



		if (dmi_walk_early(dmi_decode) == 0) {

			pr_info("SMBIOS %d.%d present.\n",

				dmi_ver >> 8, dmi_ver & 0xFF);