charset: fixed a problem with the global use of the iconv_convenience structure

We had a crash bug where a cached copy of a iconv convenience pointer
was used after being freed when loadparm asked for iconv to
reload. This could happen if a python module used a iconv based
function before loadparm was completed.

The fix is to ensure that any use of this pointer remains valid, by
reusing the pointer itself when it has already been initialised, but
filling in the child elements with the updated values.

3 files changed, 39 insertions, 13 deletions

diff --git a/lib/util/charset/charcnv.c b/lib/util/charset/charcnv.c
index a479f44426..efdb3ed2b3 100644
--- a/lib/util/charset/charcnv.c
+++ b/lib/util/charset/charcnv.c
@@ -39,6 +39,7 @@
  */
 
 struct smb_iconv_convenience {
+	TALLOC_CTX *child_ctx;
 	const char *unix_charset;
 	const char *dos_charset;
 	bool native_iconv;
@@ -83,22 +84,45 @@ static int close_iconv_convenience(struct smb_iconv_convenience *data)
 	return 0;
 }
 
-_PUBLIC_ struct smb_iconv_convenience *smb_iconv_convenience_init(TALLOC_CTX *mem_ctx,
-							 const char *dos_charset,
-							 const char *unix_charset,
-							 bool native_iconv)
+/*
+  the old_ic is passed in here as the smb_iconv_convenience structure
+  is used as a global pointer in some places (eg. python modules). We
+  don't want to invalidate those global pointers, but we do want to
+  update them with the right charset information when loadparm
+  runs. To do that we need to re-use the structure pointer, but
+  re-fill the elements in the structure with the updated values
+ */
+_PUBLIC_ struct smb_iconv_convenience *smb_iconv_convenience_reinit(TALLOC_CTX *mem_ctx,
+								    const char *dos_charset,
+								    const char *unix_charset,
+								    bool native_iconv,
+								    struct smb_iconv_convenience *old_ic)
 {
-	struct smb_iconv_convenience *ret = talloc_zero(mem_ctx, 
-					struct smb_iconv_convenience);
+	struct smb_iconv_convenience *ret;
 
+	if (old_ic != NULL) {
+		ret = old_ic;
+		close_iconv_convenience(ret);
+		talloc_free(ret->child_ctx);
+		ZERO_STRUCTP(ret);
+	} else {
+		ret = talloc_zero(mem_ctx, struct smb_iconv_convenience);
+	}
 	if (ret == NULL) {
 		return NULL;
 	}
 
+	/* we use a child context to allow us to free all ptrs without
+	   freeing the structure itself */
+	ret->child_ctx = talloc_new(ret);
+	if (ret->child_ctx == NULL) {
+		return NULL;
+	}
+
 	talloc_set_destructor(ret, close_iconv_convenience);
 
-	ret->dos_charset = talloc_strdup(ret, dos_charset);
-	ret->unix_charset = talloc_strdup(ret, unix_charset);
+	ret->dos_charset = talloc_strdup(ret->child_ctx, dos_charset);
+	ret->unix_charset = talloc_strdup(ret->child_ctx, unix_charset);
 	ret->native_iconv = native_iconv;
 
 	return ret;
diff --git a/lib/util/charset/charset.h b/lib/util/charset/charset.h
index 2c8aa41ad5..cc57b3eb54 100644
--- a/lib/util/charset/charset.h
+++ b/lib/util/charset/charset.h
@@ -163,10 +163,11 @@ codepoint_t tolower_m(codepoint_t val);
 int codepoint_cmpi(codepoint_t c1, codepoint_t c2);
 
 /* Iconv convenience functions */
-struct smb_iconv_convenience *smb_iconv_convenience_init(TALLOC_CTX *mem_ctx,
-							 const char *dos_charset,
-							 const char *unix_charset,
-							 bool native_iconv);
+struct smb_iconv_convenience *smb_iconv_convenience_reinit(TALLOC_CTX *mem_ctx,
+							   const char *dos_charset,
+							   const char *unix_charset,
+							   bool native_iconv,
+							   struct smb_iconv_convenience *old_ic);
 
 bool convert_string_convenience(struct smb_iconv_convenience *ic,
 				charset_t from, charset_t to,
diff --git a/lib/util/charset/util_unistr.c b/lib/util/charset/util_unistr.c
index f8207261c5..520ce05468 100644
--- a/lib/util/charset/util_unistr.c
+++ b/lib/util/charset/util_unistr.c
@@ -26,7 +26,8 @@ struct smb_iconv_convenience *global_iconv_convenience = NULL;
 static inline struct smb_iconv_convenience *get_iconv_convenience(void)
 {
 	if (global_iconv_convenience == NULL)
-		global_iconv_convenience = smb_iconv_convenience_init(talloc_autofree_context(), "ASCII", "UTF-8", true);
+		global_iconv_convenience = smb_iconv_convenience_reinit(talloc_autofree_context(),
+									"ASCII", "UTF-8", true, NULL);
 	return global_iconv_convenience;
 }