[dmidecode] [PATCH v2] dmidecode: Fortify entry point length checks

[Jean Delvare]

Ensure that the SMBIOS entry point is long enough to include all the
fields we need. Otherwise it is pointless to even attempt to verify
its checksum.

A similar check was added to the SMBIOS entry point parser in the
Linux kernel.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
---
Changes since v1:
 * Accept length 0x1E for 32-bit SMBIOS entry points, and add a comment
   explaining why.

 dmidecode.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- dmidecode.orig/dmidecode.c
+++ dmidecode/dmidecode.c
@@ -5700,7 +5700,8 @@ static int smbios3_decode(u8 *buf, const
                return 0;
        }
 
-       if (!checksum(buf, buf[0x06]))
+       if (buf[0x06] < 0x18
+        || !checksum(buf, buf[0x06]))
                return 0;
 
        ver = (buf[0x07] << 16) + (buf[0x08] << 8) + buf[0x09];
@@ -5747,7 +5748,12 @@ static int smbios_decode(u8 *buf, const
                return 0;
        }
 
-       if (!checksum(buf, buf[0x05])
+       /*
+        * The size of this structure is 0x1F bytes, but we also accept value
+        * 0x1E due to a mistake in SMBIOS specification version 2.1.
+        */
+       if (buf[0x05] < 0x1E
+        || !checksum(buf, buf[0x05])
         || memcmp(buf + 0x10, "_DMI_", 5) != 0
         || !checksum(buf + 0x10, 0x0F))
                return 0;


-- 
Jean Delvare
SUSE L3 Support