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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Jean Delvare <jdelvare@suse.de>,
        Parag Warudkar <parag.warudkar@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL for 4.14 118/161] firmware: dmi_scan: Fix handling of
 empty DMI strings
Thread-Topic: [PATCH AUTOSEL for 4.14 118/161] firmware: dmi_scan: Fix
 handling of empty DMI strings
Thread-Index: AQHTz5i0NNcQ1qS7T0qWOz+1IQsXGg==
Date:   Mon, 9 Apr 2018 00:21:30 +0000
Message-ID: <20180409001936.162706-118-alexander.levin@microsoft.com>
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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[] =3D "        ";
+static const char dmi_empty_string[] =3D "";
=20
 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 =3D ((u8 *) dm) + dm->length;
+	const u8 *nsp;
=20
 	if (s) {
-		s--;
-		while (s > 0 && *bp) {
+		while (--s > 0 && *bp)
 			bp +=3D strlen(bp) + 1;
-			s--;
-		}
-
-		if (*bp !=3D 0) {
-			size_t len =3D strlen(bp)+1;
-			size_t cmp_len =3D len > 8 ? 8 : len;
=20
-			if (!memcmp(bp, dmi_empty_string, cmp_len))
-				return dmi_empty_string;
+		/* Strings containing only spaces are considered empty */
+		nsp =3D bp;
+		while (*nsp =3D=3D ' ')
+			nsp++;
+		if (*nsp !=3D '\0')
 			return bp;
-		}
 	}
=20
-	return "";
+	return dmi_empty_string;
 }
=20
 static const char * __init dmi_string(const struct dmi_header *dm, u8 s)
--=20
2.15.1