Fix bug 8040 - smbclient segfaults when a Cyrillic netbios name or workgroup is configured.

As discovered by David Disseldorp <ddiss@suse.de>, convert_string_talloc()
doesn't always return consistent results for a zero length string. The
API states an incoming string must *always* contain the terminating null,
but unfotunately too much code expects passing in a zero source length
to return a null terminated string, so at least ensure we return a
correct null string in the required character set and return the
correct length.

Also ensure we cannot return a zero length for a converted string
(we ensure that the returned buffer is always allocated and zero
terminated anyway) as calling code depends on the fact that returning
true from this function will *always* return a non-zero length (as
it must include the terminating null).

Note this is a different fix from what went into master (this is
identical to the fix I'm planning for 3.5.x) as convert_string_talloc()
has diverged between the two.

Jeremy.
(cherry picked from commit bb3ed43584e6d2c4d64b5f7b9e70a7db7f3e859d)

1 files changed, 22 insertions, 2 deletions

diff --git a/source3/lib/charcnv.c b/source3/lib/charcnv.c
index 718f8108e57..743f748669a 100644
--- a/source3/lib/charcnv.c
+++ b/source3/lib/charcnv.c
@@ -573,14 +573,24 @@ bool convert_string_talloc(TALLOC_CTX *ctx, charset_t from, charset_t to,
 		errno = EINVAL;
 		return false;
 	}
+
 	if (srclen == 0) {
-		ob = talloc_strdup(ctx, "");
+		/* We really should treat this as an error, but
+		   there are too many callers that need this to
+		   return a NULL terminated string in the correct
+		   character set. */
+		if (to == CH_UTF16LE|| to == CH_UTF16BE || to == CH_UTF16MUNGED) {
+			destlen = 2;
+		} else {
+			destlen = 1;
+		}
+		ob = talloc_zero_array(ctx, char, destlen);
 		if (ob == NULL) {
 			errno = ENOMEM;
 			return false;
 		}
+		*converted_size = destlen;
 		*dest = ob;
-		*converted_size = 0;
 		return true;
 	}
 
@@ -677,6 +687,16 @@ bool convert_string_talloc(TALLOC_CTX *ctx, charset_t from, charset_t to,
 	ob[destlen] = '\0';
 	ob[destlen+1] = '\0';
 
+	/* Ensure we can never return a *converted_size of zero. */
+	if (destlen == 0) {
+		/* This can happen from a bad iconv "use_as_is:" call. */
+		if (to == CH_UTF16LE|| to == CH_UTF16BE || to == CH_UTF16MUNGED) {
+			destlen = 2;
+		} else {
+			destlen = 1;
+		}
+	}
+
 	*converted_size = destlen;
 	return true;