cifs: add replacement for cifs_strtoUCS_le called cifs_from_ucs2

Add a replacement function for cifs_strtoUCS_le. cifs_from_ucs2
takes args for the source and destination length so that we can ensure
that the function is confined within the intended buffers.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>

2 files changed, 126 insertions, 0 deletions

diff --git a/fs/cifs/cifs_unicode.c b/fs/cifs/cifs_unicode.c
index 7d75272a6b3f..8389f359b03d 100644
--- a/fs/cifs/cifs_unicode.c
+++ b/fs/cifs/cifs_unicode.c
@@ -26,6 +26,130 @@
 #include "cifs_debug.h"
 
 /*
+ * cifs_mapchar - convert a little-endian char to proper char in codepage
+ * @target - where converted character should be copied
+ * @src_char - 2 byte little-endian source character
+ * @cp - codepage to which character should be converted
+ * @mapchar - should character be mapped according to mapchars mount option?
+ *
+ * This function handles the conversion of a single character. It is the
+ * responsibility of the caller to ensure that the target buffer is large
+ * enough to hold the result of the conversion (at least NLS_MAX_CHARSET_SIZE).
+ */
+static int
+cifs_mapchar(char *target, const __le16 src_char, const struct nls_table *cp,
+             bool mapchar)
+{
+        int len = 1;
+
+        if (!mapchar)
+                goto cp_convert;
+
+        /*
+         * BB: Cannot handle remapping UNI_SLASH until all the calls to
+         *     build_path_from_dentry are modified, as they use slash as
+         *     separator.
+         */
+        switch (le16_to_cpu(src_char)) {
+        case UNI_COLON:
+                *target = ':';
+                break;
+        case UNI_ASTERIK:
+                *target = '*';
+                break;
+        case UNI_QUESTION:
+                *target = '?';
+                break;
+        case UNI_PIPE:
+                *target = '|';
+                break;
+        case UNI_GRTRTHAN:
+                *target = '>';
+                break;
+        case UNI_LESSTHAN:
+                *target = '<';
+                break;
+        default:
+                goto cp_convert;
+        }
+
+out:
+        return len;
+
+cp_convert:
+        len = cp->uni2char(le16_to_cpu(src_char), target,
+                           NLS_MAX_CHARSET_SIZE);
+        if (len <= 0) {
+                *target = '?';
+                len = 1;
+        }
+        goto out;
+}
+
+/*
+ * cifs_from_ucs2 - convert utf16le string to local charset
+ * @to - destination buffer
+ * @from - source buffer
+ * @tolen - destination buffer size (in bytes)
+ * @fromlen - source buffer size (in bytes)
+ * @codepage - codepage to which characters should be converted
+ * @mapchar - should characters be remapped according to the mapchars option?
+ *
+ * Convert a little-endian ucs2le string (as sent by the server) to a string
+ * in the provided codepage. The tolen and fromlen parameters are to ensure
+ * that the code doesn't walk off of the end of the buffer (which is always
+ * a danger if the alignment of the source buffer is off). The destination
+ * string is always properly null terminated and fits in the destination
+ * buffer. Returns the length of the destination string in bytes (including
+ * null terminator).
+ *
+ * Note that some windows versions actually send multiword UTF-16 characters
+ * instead of straight UCS-2. The linux nls routines however aren't able to
+ * deal with those characters properly. In the event that we get some of
+ * those characters, they won't be translated properly.
+ */
+int
+cifs_from_ucs2(char *to, const __le16 *from, int tolen, int fromlen,
+                 const struct nls_table *codepage, bool mapchar)
+{
+        int i, charlen, safelen;
+        int outlen = 0;
+        int nullsize = nls_nullsize(codepage);
+        int fromwords = fromlen / 2;
+        char tmp[NLS_MAX_CHARSET_SIZE];
+
+        /*
+         * because the chars can be of varying widths, we need to take care
+         * not to overflow the destination buffer when we get close to the
+         * end of it. Until we get to this offset, we don't need to check
+         * for overflow however.
+         */
+        safelen = tolen - (NLS_MAX_CHARSET_SIZE + nullsize);
+
+        for (i = 0; i < fromwords && from[i]; i++) {
+                /*
+                 * check to see if converting this character might make the
+                 * conversion bleed into the null terminator
+                 */
+                if (outlen >= safelen) {
+                        charlen = cifs_mapchar(tmp, from[i], codepage, mapchar);
+                        if ((outlen + charlen) > (tolen - nullsize))
+                                break;
+                }
+
+                /* put converted char into 'to' buffer */
+                charlen = cifs_mapchar(&to[outlen], from[i], codepage, mapchar);
+                outlen += charlen;
+        }
+
+        /* properly null-terminate string */
+        for (i = 0; i < nullsize; i++)
+                to[outlen++] = 0;
+
+        return outlen;
+}
+
+/*
  * NAME:        cifs_strfromUCS()
  *
  * FUNCTION:    Convert little-endian unicode string to character string
diff --git a/fs/cifs/cifs_unicode.h b/fs/cifs/cifs_unicode.h
index d6fe8ecd1ffc..6aa6533e49fa 100644
--- a/fs/cifs/cifs_unicode.h
+++ b/fs/cifs/cifs_unicode.h
@@ -72,6 +72,8 @@ extern struct UniCaseRange UniLowerRange[];
 #endif                          /* UNIUPR_NOLOWER */
 
 #ifdef __KERNEL__
+int cifs_from_ucs2(char *to, const __le16 *from, int tolen, int fromlen,
+                   const struct nls_table *codepage, bool mapchar);
 int cifs_strfromUCS_le(char *, const __le16 *, int, const struct nls_table *);
 int cifs_strtoUCS(__le16 *, const char *, int, const struct nls_table *);
 #endif