CVE-2013-1773 (published 2013-02-28T19:55Z)

Buffer overflow in the VFAT filesystem implementation in the Linux kernel before 3.3 allows local users to gain privileges or cause a denial of service (system crash) via a VFAT write operation on a filesystem with the utf8 mount option, which is not properly handled during UTF-8 to UTF-16 conversion.

Severity: MEDIUM
CVSS v2 base score: 6.2 (AV:L/AC:H/Au:N/C:C/I:C/A:C)

Weakness information:
cwe_id: CWE-119
cwe_name: Improper Restriction of Operations within the Bounds of a Memory Buffer
description: The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
extended_description: 
            Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced. This can cause read or write operations to be performed on memory locations that may be associated with other variables, data structures, or internal program data.
         
         

Fix information:
repo_url: https://github.com/torvalds/linux
commit_details: repo_url: https://github.com/torvalds/linux
author: Alan Stern
author_date: 2011-11-17 16:42:19-05:00
msg: NLS: improve UTF8 -> UTF16 string conversion routine

The utf8s_to_utf16s conversion routine needs to be improved.  Unlike
its utf16s_to_utf8s sibling, it doesn't accept arguments specifying
the maximum length of the output buffer or the endianness of its
16-bit output.

This patch (as1501) adds the two missing arguments, and adjusts the
only two places in the kernel where the function is called.  A
follow-on patch will add a third caller that does utilize the new
capabilities.

The two conversion routines are still annoyingly inconsistent in the
way they handle invalid byte combinations.  But that's a subject for a
different patch.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
repository: repo_url: https://github.com/torvalds/linux
repo_name: torvalds/linux
description: Linux kernel source tree
repo_language: C
owner: torvalds
file_changes: filename: hv_kvp.c
change_type: ModificationType.MODIFY
diff: @@ -212,11 +212,13 @@ kvp_respond_to_host(char *key, char *value, int error)
 	 * The windows host expects the key/value pair to be encoded
 	 * in utf16.
 	 */
-	keylen = utf8s_to_utf16s(key_name, strlen(key_name),
-				(wchar_t *)kvp_data->data.key);
+	keylen = utf8s_to_utf16s(key_name, strlen(key_name), UTF16_HOST_ENDIAN,
+				(wchar_t *) kvp_data->data.key,
+				HV_KVP_EXCHANGE_MAX_KEY_SIZE / 2);
 	kvp_data->data.key_size = 2*(keylen + 1); /* utf16 encoding */
-	valuelen = utf8s_to_utf16s(value, strlen(value),
-				(wchar_t *)kvp_data->data.value);
+	valuelen = utf8s_to_utf16s(value, strlen(value), UTF16_HOST_ENDIAN,
+				(wchar_t *) kvp_data->data.value,
+				HV_KVP_EXCHANGE_MAX_VALUE_SIZE / 2);
 	kvp_data->data.value_size = 2*(valuelen + 1); /* utf16 encoding */
 
 	kvp_data->data.value_type = REG_SZ; /* all our values are strings */

programming_language: C
filename: namei_vfat.c
change_type: ModificationType.MODIFY
diff: @@ -512,7 +512,8 @@ xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,
 	int charlen;
 
 	if (utf8) {
-		*outlen = utf8s_to_utf16s(name, len, (wchar_t *)outname);
+		*outlen = utf8s_to_utf16s(name, len, UTF16_HOST_ENDIAN,
+				(wchar_t *) outname, FAT_LFN_LEN + 2);
 		if (*outlen < 0)
 			return *outlen;
 		else if (*outlen > FAT_LFN_LEN)

programming_language: C
filename: nls_base.c
change_type: ModificationType.MODIFY
diff: @@ -114,34 +114,57 @@ int utf32_to_utf8(unicode_t u, u8 *s, int maxlen)
 }
 EXPORT_SYMBOL(utf32_to_utf8);
 
-int utf8s_to_utf16s(const u8 *s, int len, wchar_t *pwcs)
+static inline void put_utf16(wchar_t *s, unsigned c, enum utf16_endian endian)
+{
+	switch (endian) {
+	default:
+		*s = (wchar_t) c;
+		break;
+	case UTF16_LITTLE_ENDIAN:
+		*s = __cpu_to_le16(c);
+		break;
+	case UTF16_BIG_ENDIAN:
+		*s = __cpu_to_be16(c);
+		break;
+	}
+}
+
+int utf8s_to_utf16s(const u8 *s, int len, enum utf16_endian endian,
+		wchar_t *pwcs, int maxlen)
 {
 	u16 *op;
 	int size;
 	unicode_t u;
 
 	op = pwcs;
-	while (*s && len > 0) {
+	while (len > 0 && maxlen > 0 && *s) {
 		if (*s & 0x80) {
 			size = utf8_to_utf32(s, len, &u);
 			if (size < 0)
 				return -EINVAL;
+			s += size;
+			len -= size;
 
 			if (u >= PLANE_SIZE) {
+				if (maxlen < 2)
+					break;
 				u -= PLANE_SIZE;
-				*op++ = (wchar_t) (SURROGATE_PAIR |
-						((u >> 10) & SURROGATE_BITS));
-				*op++ = (wchar_t) (SURROGATE_PAIR |
+				put_utf16(op++, SURROGATE_PAIR |
+						((u >> 10) & SURROGATE_BITS),
+						endian);
+				put_utf16(op++, SURROGATE_PAIR |
 						SURROGATE_LOW |
-						(u & SURROGATE_BITS));
+						(u & SURROGATE_BITS),
+						endian);
+				maxlen -= 2;
 			} else {
-				*op++ = (wchar_t) u;
+				put_utf16(op++, u, endian);
+				maxlen--;
 			}
-			s += size;
-			len -= size;
 		} else {
-			*op++ = *s++;
+			put_utf16(op++, *s++, endian);
 			len--;
+			maxlen--;
 		}
 	}
 	return op - pwcs;

programming_language: C
filename: nls.h
change_type: ModificationType.MODIFY
diff: @@ -43,7 +43,7 @@ enum utf16_endian {
 	UTF16_BIG_ENDIAN
 };
 
-/* nls.c */
+/* nls_base.c */
 extern int register_nls(struct nls_table *);
 extern int unregister_nls(struct nls_table *);
 extern struct nls_table *load_nls(char *);
@@ -52,7 +52,8 @@ extern struct nls_table *load_nls_default(void);
 
 extern int utf8_to_utf32(const u8 *s, int len, unicode_t *pu);
 extern int utf32_to_utf8(unicode_t u, u8 *s, int maxlen);
-extern int utf8s_to_utf16s(const u8 *s, int len, wchar_t *pwcs);
+extern int utf8s_to_utf16s(const u8 *s, int len,
+		enum utf16_endian endian, wchar_t *pwcs, int maxlen);
 extern int utf16s_to_utf8s(const wchar_t *pwcs, int len,
 		enum utf16_endian endian, u8 *s, int maxlen);
 

programming_language: C