use xmallocz to avoid size arithmetic

We frequently allocate strings as xmalloc(len + 1), where
the extra 1 is for the NUL terminator. This can be done more
simply with xmallocz, which also checks for integer
overflow.

There's no case where switching xmalloc(n+1) to xmallocz(n)
is wrong; the result is the same length, and malloc made no
guarantees about what was in the buffer anyway. But in some
cases, we can stop manually placing NUL at the end of the
allocated buffer. But that's only safe if it's clear that
the contents will always fill the buffer.

In each case where this patch does so, I manually examined
the control flow, and I tried to err on the side of caution.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

15 files changed, 17 insertions, 25 deletions

diff --git a/builtin/check-ref-format.c b/builtin/check-ref-format.c
index fd915d5984..eac499450f 100644
--- a/builtin/check-ref-format.c
+++ b/builtin/check-ref-format.c
@@ -20,7 +20,7 @@ static const char builtin_check_ref_format_usage[] =
  */
 static char *collapse_slashes(const char *refname)
 {
-	char *ret = xmalloc(strlen(refname) + 1);
+	char *ret = xmallocz(strlen(refname));
 	char ch;
 	char prev = '/';
 	char *cp = ret;
diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index d4f0cbd451..ca570041df 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -174,7 +174,7 @@ static struct merge_list *create_entry(unsigned stage, unsigned mode, const unsi
 
 static char *traverse_path(const struct traverse_info *info, const struct name_entry *n)
 {
-	char *path = xmalloc(traverse_path_len(info, n) + 1);
+	char *path = xmallocz(traverse_path_len(info, n));
 	return make_traverse_path(path, info, n);
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 475b9581a5..0a45710be8 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -52,7 +52,7 @@ static int prune_worktree(const char *id, struct strbuf *reason)
 		return 1;
 	}
 	len = st.st_size;
-	path = xmalloc(len + 1);
+	path = xmallocz(len);
 	read_in_full(fd, path, len);
 	close(fd);
 	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
diff --git a/column.c b/column.c
index f9fda681f1..d55ead18ef 100644
--- a/column.c
+++ b/column.c
@@ -173,9 +173,8 @@ static void display_table(const struct string_list *list,
 	if (colopts & COL_DENSE)
 		shrink_columns(&data);
 
-	empty_cell = xmalloc(initial_width + 1);
+	empty_cell = xmallocz(initial_width);
 	memset(empty_cell, ' ', initial_width);
-	empty_cell[initial_width] = '\0';
 	for (y = 0; y < data.rows; y++) {
 		for (x = 0; x < data.cols; x++)
 			if (display_cell(&data, initial_width, empty_cell, x, y))
diff --git a/combine-diff.c b/combine-diff.c
index a698016db7..890c4157bd 100644
--- a/combine-diff.c
+++ b/combine-diff.c
@@ -1043,7 +1043,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 				elem->mode = canon_mode(S_IFLNK);
 
 			result_size = len;
-			result = xmalloc(len + 1);
+			result = xmallocz(len);
 
 			done = read_in_full(fd, result, len);
 			if (done < 0)
@@ -1051,8 +1051,6 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 			else if (done < len)
 				die("early EOF '%s'", elem->path);
 
-			result[len] = 0;
-
 			/* If not a fake symlink, apply filters, e.g. autocrlf */
 			if (is_file) {
 				struct strbuf buf = STRBUF_INIT;
diff --git a/config.c b/config.c
index 86a5eb2571..ba8fd13765 100644
--- a/config.c
+++ b/config.c
@@ -1878,7 +1878,7 @@ static int git_config_parse_key_1(const char *key, char **store_key, int *basele
 	 * Validate the key and while at it, lower case it for matching.
 	 */
 	if (store_key)
-		*store_key = xmalloc(strlen(key) + 1);
+		*store_key = xmallocz(strlen(key));
 
 	dot = 0;
 	for (i = 0; key[i]; i++) {
@@ -1902,8 +1902,6 @@ static int git_config_parse_key_1(const char *key, char **store_key, int *basele
 		if (store_key)
 			(*store_key)[i] = c;
 	}
-	if (store_key)
-		(*store_key)[i] = 0;
 
 	return 0;
 
diff --git a/dir.c b/dir.c
index 363a402887..cb5bff8d8f 100644
--- a/dir.c
+++ b/dir.c
@@ -711,7 +711,7 @@ static int add_excludes(const char *fname, const char *base, int baselen,
 			close(fd);
 			return 0;
 		}
-		buf = xmalloc(size+1);
+		buf = xmallocz(size);
 		if (read_in_full(fd, buf, size) != size) {
 			free(buf);
 			close(fd);
diff --git a/entry.c b/entry.c
index 582c40071a..a4109574fa 100644
--- a/entry.c
+++ b/entry.c
@@ -6,7 +6,7 @@
 static void create_directories(const char *path, int path_len,
 			       const struct checkout *state)
 {
-	char *buf = xmalloc(path_len + 1);
+	char *buf = xmallocz(path_len);
 	int len = 0;
 
 	while (len < path_len) {
diff --git a/grep.c b/grep.c
index 7b2b96a437..528b652f71 100644
--- a/grep.c
+++ b/grep.c
@@ -1741,7 +1741,7 @@ static int grep_source_load_file(struct grep_source *gs)
 	i = open(filename, O_RDONLY);
 	if (i < 0)
 		goto err_ret;
-	data = xmalloc(size + 1);
+	data = xmallocz(size);
 	if (st.st_size != read_in_full(i, data, size)) {
 		error(_("'%s': short read %s"), filename, strerror(errno));
 		close(i);
@@ -1749,7 +1749,6 @@ static int grep_source_load_file(struct grep_source *gs)
 		return -1;
 	}
 	close(i);
-	data[size] = 0;
 
 	gs->buf = data;
 	gs->size = size;
diff --git a/imap-send.c b/imap-send.c
index 4d3b7737a9..2c52027c84 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -892,12 +892,11 @@ static char *cram(const char *challenge_64, const char *user, const char *pass)
 	response = xstrfmt("%s %s", user, hex);
 	resp_len = strlen(response) + 1;
 
-	response_64 = xmalloc(ENCODED_SIZE(resp_len) + 1);
+	response_64 = xmallocz(ENCODED_SIZE(resp_len));
 	encoded_len = EVP_EncodeBlock((unsigned char *)response_64,
 				      (unsigned char *)response, resp_len);
 	if (encoded_len < 0)
 		die("EVP_EncodeBlock error");
-	response_64[encoded_len] = '\0';
 	return (char *)response_64;
 }
 
@@ -1188,7 +1187,7 @@ static void lf_to_crlf(struct strbuf *msg)
 		j++;
 	}
 
-	new = xmalloc(j + 1);
+	new = xmallocz(j);
 
 	/*
 	 * Second pass: write the new string.  Note that this loop is
diff --git a/ll-merge.c b/ll-merge.c
index 0338630fc2..ff4a43a982 100644
--- a/ll-merge.c
+++ b/ll-merge.c
@@ -205,7 +205,7 @@ static int ll_ext_merge(const struct ll_merge_driver *fn,
 	if (fstat(fd, &st))
 		goto close_bad;
 	result->size = st.st_size;
-	result->ptr = xmalloc(result->size + 1);
+	result->ptr = xmallocz(result->size);
 	if (read_in_full(fd, result->ptr, result->size) != result->size) {
 		free(result->ptr);
 		result->ptr = NULL;
diff --git a/progress.c b/progress.c
index 353bd37416..76a88c573f 100644
--- a/progress.c
+++ b/progress.c
@@ -247,7 +247,7 @@ void stop_progress_msg(struct progress **p_progress, const char *msg)
 		size_t len = strlen(msg) + 5;
 		struct throughput *tp = progress->throughput;
 
-		bufp = (len < sizeof(buf)) ? buf : xmalloc(len + 1);
+		bufp = (len < sizeof(buf)) ? buf : xmallocz(len);
 		if (tp) {
 			unsigned int rate = !tp->avg_misecs ? 0 :
 					tp->avg_bytes / tp->avg_misecs;
diff --git a/refs.c b/refs.c
index e2d34b253e..1d9e2a7932 100644
--- a/refs.c
+++ b/refs.c
@@ -124,7 +124,7 @@ int refname_is_safe(const char *refname)
 		char *buf;
 		int result;
 
-		buf = xmalloc(strlen(refname) + 1);
+		buf = xmallocz(strlen(refname));
 		/*
 		 * Does the refname try to escape refs/?
 		 * For example: refs/foo/../bar is safe but refs/foo/../../bar
diff --git a/setup.c b/setup.c
index 2c4b22c845..669062a090 100644
--- a/setup.c
+++ b/setup.c
@@ -88,7 +88,7 @@ char *prefix_path_gently(const char *prefix, int len,
 	const char *orig = path;
 	char *sanitized;
 	if (is_absolute_path(orig)) {
-		sanitized = xmalloc(strlen(path) + 1);
+		sanitized = xmallocz(strlen(path));
 		if (remaining_prefix)
 			*remaining_prefix = 0;
 		if (normalize_path_copy_len(sanitized, path, remaining_prefix)) {
@@ -499,14 +499,13 @@ const char *read_gitfile_gently(const char *path, int *return_error_code)
 		error_code = READ_GITFILE_ERR_OPEN_FAILED;
 		goto cleanup_return;
 	}
-	buf = xmalloc(st.st_size + 1);
+	buf = xmallocz(st.st_size);
 	len = read_in_full(fd, buf, st.st_size);
 	close(fd);
 	if (len != st.st_size) {
 		error_code = READ_GITFILE_ERR_READ_FAILED;
 		goto cleanup_return;
 	}
-	buf[len] = '\0';
 	if (!starts_with(buf, "gitdir: ")) {
 		error_code = READ_GITFILE_ERR_INVALID_FORMAT;
 		goto cleanup_return;
diff --git a/strbuf.c b/strbuf.c
index d76f0aed85..de7a7c2730 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -685,7 +685,7 @@ char *xstrdup_tolower(const char *string)
 	size_t len, i;
 
 	len = strlen(string);
-	result = xmalloc(len + 1);
+	result = xmallocz(len);
 	for (i = 0; i < len; i++)
 		result[i] = tolower(string[i]);
 	result[i] = '\0';