Re: [PATCH 24/30] merge-recursive: Add computation of collisions due to dir rename & merging

["René Scharfe" <l.s.r@web.de>]

Am 10.11.2017 um 20:05 schrieb Elijah Newren:
> +static struct dir_rename_entry *check_dir_renamed(const char *path,
> +						  struct hashmap *dir_renames) {
> +	char temp[PATH_MAX];
> +	char *end;
> +	struct dir_rename_entry *entry;
> +
> +	strcpy(temp, path);
> +	while ((end = strrchr(temp, '/'))) {
> +		*end = '\0';
> +		entry = dir_rename_find_entry(dir_renames, temp);
> +		if (entry)
> +			return entry;
> +	}
> +	return NULL;
> +}

The value of PATH_MAX is platform-dependent, so it's easy to exceed when
doing cross-platform development.  It's also not a hard limit on most
operating systems, not even on Windows.  Further reading:

   https://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html

So using a fixed buffer is not a good idea, and writing to it without
checking is dangerous.  Here's a fix:

-- >8 --
Subject: [PATCH] merge-recursive: use xstrdup() instead of fixed buffer

Paths can be longer than PATH_MAX.  Avoid a buffer overrun in
check_dir_renamed() by using xstrdup() to make a private copy safely.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 merge-recursive.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index ac27abbd4c..db708176c5 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -2211,18 +2211,18 @@ static struct hashmap *get_directory_renames(struct diff_queue_struct *pairs,
 static struct dir_rename_entry *check_dir_renamed(const char *path,
 						  struct hashmap *dir_renames)
 {
-	char temp[PATH_MAX];
+	char *temp = xstrdup(path);
 	char *end;
-	struct dir_rename_entry *entry;
+	struct dir_rename_entry *entry = NULL;;
 
-	strcpy(temp, path);
 	while ((end = strrchr(temp, '/'))) {
 		*end = '\0';
 		entry = dir_rename_find_entry(dir_renames, temp);
 		if (entry)
-			return entry;
+			break;
 	}
-	return NULL;
+	free(temp);
+	return entry;
 }
 
 static void compute_collisions(struct hashmap *collisions,
-- 
2.17.1