[PATCH 5.15.y] exfat: check if filename entries exceeds max filename length

[Harshit Mogalapalli]

From: Namjae Jeon <linkinjeon@xxxxxxxxxx>

[ Upstream commit d42334578eba1390859012ebb91e1e556d51db49 ]

exfat_extract_uni_name copies characters from a given file name entry into
the 'uniname' variable. This variable is actually defined on the stack of
the exfat_readdir() function. According to the definition of
the 'exfat_uni_name' type, the file name should be limited 255 characters
(+ null teminator space), but the exfat_get_uniname_from_ext_entry()
function can write more characters because there is no check if filename
entries exceeds max filename length. This patch add the check not to copy
filename characters when exceeding max filename length.

Cc: stable@xxxxxxxxxxxxxxx
Cc: Yuezhang Mo <Yuezhang.Mo@xxxxxxxx>
Reported-by: Maxim Suhanov <dfirblog@xxxxxxxxx>
Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
Signed-off-by: Namjae Jeon <linkinjeon@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
[Harshit: backport to 5.15.y]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
---
The conflict resolved patch for 6.1.y applies cleanly to 5.15.y as
well.
Note: This fix is already present in 5.10.y but missing in 5.15.y
---
 fs/exfat/dir.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/exfat/dir.c b/fs/exfat/dir.c
index 8475a8653c3a..f6dd4fc8eaf4 100644
--- a/fs/exfat/dir.c
+++ b/fs/exfat/dir.c
@@ -34,6 +34,7 @@ static void exfat_get_uniname_from_ext_entry(struct super_block *sb,
 {
 	int i;
 	struct exfat_entry_set_cache *es;
+	unsigned int uni_len = 0, len;
 
 	es = exfat_get_dentry_set(sb, p_dir, entry, ES_ALL_ENTRIES);
 	if (!es)
@@ -52,7 +53,10 @@ static void exfat_get_uniname_from_ext_entry(struct super_block *sb,
 		if (exfat_get_entry_type(ep) != TYPE_EXTEND)
 			break;
 
-		exfat_extract_uni_name(ep, uniname);
+		len = exfat_extract_uni_name(ep, uniname);
+		uni_len += len;
+		if (len != EXFAT_FILE_NAME_LEN || uni_len >= MAX_NAME_LENGTH)
+			break;
 		uniname += EXFAT_FILE_NAME_LEN;
 	}
 
@@ -1032,7 +1036,8 @@ int exfat_find_dir_entry(struct super_block *sb, struct exfat_inode_info *ei,
 			if (entry_type == TYPE_EXTEND) {
 				unsigned short entry_uniname[16], unichar;
 
-				if (step != DIRENT_STEP_NAME) {
+				if (step != DIRENT_STEP_NAME ||
+				    name_len >= MAX_NAME_LENGTH) {
 					step = DIRENT_STEP_FILE;
 					continue;
 				}
-- 
2.34.1