[PATCH 5/8] erofs-utils: exclude: fix stack overflow when checking long paths

[Yifan Zhao <stopire@gmail.com>]

Assisted-by: Codex:gpt-6-astra
Assisted-by: Claude Code:deepseek-v4.1-flash-1017
Signed-off-by: Yifan Zhao <stopire@gmail.com>
---
 lib/exclude.c | 7 ++++++-
 lib/inode.c   | 8 +++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/lib/exclude.c b/lib/exclude.c
index 6beb46b..487da6a 100644
--- a/lib/exclude.c
+++ b/lib/exclude.c
@@ -108,7 +108,12 @@ struct erofs_exclude_rule *erofs_is_exclude_path(const char *dir,
 		/* no prefix */
 		s = name;
 	} else {
-		sprintf(buf, "%s/%s", dir, name);
+		int ret = snprintf(buf, sizeof(buf), "%s/%s", dir, name);
+
+		if (ret < 0)
+			return ERR_PTR(-errno);
+		if ((size_t)ret >= sizeof(buf))
+			return ERR_PTR(-ENAMETOOLONG);
 		s = buf;
 	}
 
diff --git a/lib/inode.c b/lib/inode.c
index 3108aa0..f687857 100644
--- a/lib/inode.c
+++ b/lib/inode.c
@@ -1851,6 +1851,7 @@ static int erofs_mkfs_import_localdir(struct erofs_importer *im, struct erofs_in
 	__nr_subdirs = *nr_subdirs;
 	__nlink = *i_nlink;
 	while (1) {
+		struct erofs_exclude_rule *rule;
 		struct erofs_inode *inode;
 		struct erofs_dentry *d;
 		char buf[PATH_MAX];
@@ -1873,7 +1874,12 @@ static int erofs_mkfs_import_localdir(struct erofs_importer *im, struct erofs_in
 			continue;
 
 		/* skip if it's a exclude file */
-		if (erofs_is_exclude_path(dir->i_srcpath, dp->d_name))
+		rule = erofs_is_exclude_path(dir->i_srcpath, dp->d_name);
+		if (IS_ERR(rule)) {
+			ret = PTR_ERR(rule);
+			goto err_closedir;
+		}
+		if (rule)
 			continue;
 
 		d = erofs_d_alloc(dir, dp->d_name);
-- 
2.56.0