[PATCH] erofs-utils: fsck: block insane long paths when extracting images

[Gao Xiang]

Since some crafted EROFS filesystem images could have insane deep
hierarchy (or may cause directory loops) which triggers the
PATH_MAX-sized path buffer OR stack overflow.

Actually such crafted images cannot be deemed as real corrupted
images but over-PATH_MAX paths are not something that we'd like to
support for now.

CVE: CVE-2023-33551
Closes: https://nvd.nist.gov/vuln/detail/CVE-2023-33551
Reported-by: Chaoming Yang <lometsj at live.com>
Fixes: f44043561491 ("erofs-utils: introduce fsck.erofs")
Fixes: b11f84f593f9 ("erofs-utils: fsck: convert to use erofs_iterate_dir()")
Fixes: 412c8f908132 ("erofs-utils: fsck: add --extract=X support to extract to path X")
Signeo-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 fsck/main.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/fsck/main.c b/fsck/main.c
index 52fb7a0..3d1682c 100644
--- a/fsck/main.c
+++ b/fsck/main.c
@@ -680,28 +680,35 @@ again:
 static int erofsfsck_dirent_iter(struct erofs_dir_context *ctx)
 {
 	int ret;
-	size_t prev_pos = fsckcfg.extract_pos;
+	size_t prev_pos, curr_pos;
 
 	if (ctx->dot_dotdot)
 		return 0;
 
-	if (fsckcfg.extract_path) {
-		size_t curr_pos = prev_pos;
+	prev_pos = fsckcfg.extract_pos;
+	curr_pos = prev_pos;
+
+	if (prev_pos + ctx->de_namelen >= PATH_MAX) {
+		erofs_err("unable to fsck since the path is too long (%u)",
+			  curr_pos + ctx->de_namelen);
+		return -EOPNOTSUPP;
+	}
 
+	if (fsckcfg.extract_path) {
 		fsckcfg.extract_path[curr_pos++] = '/';
 		strncpy(fsckcfg.extract_path + curr_pos, ctx->dname,
 			ctx->de_namelen);
 		curr_pos += ctx->de_namelen;
 		fsckcfg.extract_path[curr_pos] = '\0';
-		fsckcfg.extract_pos = curr_pos;
+	} else {
+		curr_pos += ctx->de_namelen;
 	}
-
+	fsckcfg.extract_pos = curr_pos;
 	ret = erofsfsck_check_inode(ctx->dir->nid, ctx->de_nid);
 
-	if (fsckcfg.extract_path) {
+	if (fsckcfg.extract_path)
 		fsckcfg.extract_path[prev_pos] = '\0';
-		fsckcfg.extract_pos = prev_pos;
-	}
+	fsckcfg.extract_pos = prev_pos;
 	return ret;
 }
 
-- 
2.24.4