[PATCH AUTOSEL for 4.14 118/161] firmware: dmi_scan: Fix handling of empty DMI strings

Sasha Levin
2018-04-09T03:02:30Z

From: Jean Delvare <jdelvare@suse.de>

[ Upstream commit a7770ae194569e96a93c48aceb304edded9cc648 ]

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: 79da4721117f ("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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
drivers/firmware/dmi_scan.c | 22 +++++++++-------------
1 file changed, 9 insertions(+), 13 deletions(-)

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 783041964439..e8db9659a36b 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -18,7 +18,7 @@ EXPORT_SYMBOL_GPL(dmi_kobj);
* of and an antecedent to, SMBIOS, which stands for System
* Management BIOS. See further: http://www.dmtf.org/standards
*/
-static const char dmi_empty_string[] = " ";
+static const char dmi_empty_string[] = "";

static u32 dmi_ver __initdata;
static u32 dmi_len;
@@ -44,25 +44,21 @@ 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)
--
2.15.1