Commit a7770ae1 authored Feb 03, 2018 by Jean Delvare

firmware: dmi_scan: Fix handling of empty DMI strings



The handling of empty DMI strings looks quite broken to me:
* Strings from 1 to 7 spaces are not considered empty.
* True empty DMI strings (string index set to 0) are not considered
  empty, and result in allocating a 0-char string.
* Strings with invalid index also result in allocating a 0-char
  string.
* Strings starting with 8 spaces are all considered empty, even if
  non-space characters follow (sounds like a weird thing to do, but
  I have actually seen occurrences of this in DMI tables before.)
* Strings which are considered empty are reported as 8 spaces,
  instead of being actually empty.

Some of these issues are the result of an off-by-one error in memcmp,
the rest is incorrect by design.

So let's get it square: missing strings and strings made of only
spaces, regardless of their length, should be treated as empty and
no memory should be allocated for them. All other strings are
non-empty and should be allocated.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Fixes: 79da4721 ("x86: fix DMI out of memory problems")
Cc: Parag Warudkar <parag.warudkar@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

parent 7117794f

drivers/firmware/dmi_scan.c

+9 −13

Original line number	Diff line number	Diff line
		@@ -39,25 +39,21 @@ static int dmi_memdev_nr;
		static const char * __init dmi_string_nosave(const struct dmi_header *dm, u8 s)
		{
		const u8 bp = ((u8 ) dm) + dm->length;
		const u8 *nsp;

		if (s) {
		s--;
		while (s > 0 && *bp) {
		while (--s > 0 && *bp)
		bp += strlen(bp) + 1;
		s--;
		}

		if (*bp != 0) {
		size_t len = strlen(bp)+1;
		size_t cmp_len = len > 8 ? 8 : len;

		if (!memcmp(bp, dmi_empty_string, cmp_len))
		return dmi_empty_string;
		/* Strings containing only spaces are considered empty */
		nsp = bp;
		while (*nsp == ' ')
		nsp++;
		if (*nsp != '\0')
		return bp;
		}
		}

		return "";
		return dmi_empty_string;
		}

		static const char * __init dmi_string(const struct dmi_header *dm, u8 s)

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