From 8e4a702a1f96f118976da6eb9ece344df625eabb Mon Sep 17 00:00:00 2001
From: Timo Sirainen <tss@iki.fi>
Date: Tue, 15 Jan 2013 08:30:03 +0200
Subject: [PATCH] buffer: Always keep +1 byte available for str_c()'s NUL.

---
 src/lib/Makefile.am |  1 +
 src/lib/buffer.c    | 11 +++++++++--
 src/lib/str.c       |  3 ---
 src/lib/test-lib.c  |  1 +
 src/lib/test-lib.h  |  1 +
 src/lib/test-str.c  | 26 ++++++++++++++++++++++++++
 6 files changed, 38 insertions(+), 5 deletions(-)
 create mode 100644 src/lib/test-str.c

diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index eeccfd86fd..ebb025f58b 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -268,6 +268,7 @@ test_lib_SOURCES = \
 	test-primes.c \
 	test-priorityq.c \
 	test-seq-range-array.c \
+	test-str.c \
 	test-strescape.c \
 	test-strfuncs.c \
 	test-str-find.c \
diff --git a/src/lib/buffer.c b/src/lib/buffer.c
index e056da9e87..c73bc0340b 100644
--- a/src/lib/buffer.c
+++ b/src/lib/buffer.c
@@ -39,6 +39,7 @@ static void buffer_alloc(struct real_buffer *buf, size_t size)
 static inline void
 buffer_check_limits(struct real_buffer *buf, size_t pos, size_t data_size)
 {
+	unsigned int extra;
 	size_t new_size;
 
 	if (unlikely((size_t)-1 - pos < data_size)) {
@@ -53,7 +54,13 @@ buffer_check_limits(struct real_buffer *buf, size_t pos, size_t data_size)
 
 		memset(buf->w_buffer + buf->used, 0, max - buf->used);
 	}
-	if (new_size > buf->alloc) {
+
+	/* always keep +1 byte allocated available in case str_c() is called
+	   for this buffer. this is mainly for cases where the buffer is
+	   allocated from data stack, and str_c() is called in a separate stack
+	   frame. */
+	extra = buf->dynamic ? 1 : 0;
+	if (new_size + extra > buf->alloc) {
 		if (unlikely(!buf->dynamic)) {
 			i_panic("Buffer full (%"PRIuSIZE_T" > %"PRIuSIZE_T", "
 				"pool %s)", pos + data_size, buf->alloc,
@@ -62,7 +69,7 @@ buffer_check_limits(struct real_buffer *buf, size_t pos, size_t data_size)
 		}
 
 		buffer_alloc(buf, pool_get_exp_grown_size(buf->pool, buf->alloc,
-							  new_size));
+							  new_size + extra));
 	}
 #if 0
 	else if (new_size > buf->used && buf->alloced &&
diff --git a/src/lib/str.c b/src/lib/str.c
index 0f9d6ce244..719d8d0eda 100644
--- a/src/lib/str.c
+++ b/src/lib/str.c
@@ -45,9 +45,6 @@ static void str_add_nul(string_t *str)
 	size_t len = str_len(str);
 	size_t alloc = buffer_get_size(str);
 
-#ifdef DEBUG
-	buffer_verify_pool(str);
-#endif
 	if (len == alloc || data[len] != '\0') {
 		buffer_write(str, len, "", 1);
 		/* remove the \0 - we don't want to keep it */
diff --git a/src/lib/test-lib.c b/src/lib/test-lib.c
index ca6f223f3d..21c3b84c83 100644
--- a/src/lib/test-lib.c
+++ b/src/lib/test-lib.c
@@ -25,6 +25,7 @@ int main(void)
 		test_primes,
 		test_priorityq,
 		test_seq_range_array,
+		test_str,
 		test_strescape,
 		test_strfuncs,
 		test_str_find,
diff --git a/src/lib/test-lib.h b/src/lib/test-lib.h
index c7cc7b9e36..206ef4d5f5 100644
--- a/src/lib/test-lib.h
+++ b/src/lib/test-lib.h
@@ -24,6 +24,7 @@ void test_ostream_file(void);
 void test_primes(void);
 void test_priorityq(void);
 void test_seq_range_array(void);
+void test_str(void);
 void test_strescape(void);
 void test_strfuncs(void);
 void test_str_find(void);
diff --git a/src/lib/test-str.c b/src/lib/test-str.c
new file mode 100644
index 0000000000..deb4b7470d
--- /dev/null
+++ b/src/lib/test-str.c
@@ -0,0 +1,26 @@
+/* Copyright (c) 2012 Dovecot authors, see the included COPYING file */
+
+#include "test-lib.h"
+#include "str.h"
+
+static void test_str_c(void)
+{
+	string_t *str;
+	unsigned int i, j;
+
+	test_begin("str_c()");
+	for (i = 0; i < 32; i++) T_BEGIN {
+		str = t_str_new(15);
+		for (j = 0; j < i; j++)
+			str_append_c(str, 'x');
+		T_BEGIN {
+			(void)str_c(str);
+		} T_END;
+	} T_END;
+	test_end();
+}
+
+void test_str(void)
+{
+	test_str_c();
+}
-- 
2.47.3