[SRU][Jammy/Jammy-OEM-6.0/Jammy-OEM-6.1][PATCH 1/1] exfat: check if filename entries exceeds max filename length

[Yuxuan Luo]

From: Namjae Jeon <linkinjeon at kernel.org>

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 at vger.kernel.org
Cc: Yuezhang Mo <Yuezhang.Mo at sony.com>
Reported-by: Maxim Suhanov <dfirblog at gmail.com>
Reviewed-by: Sungjong Seo <sj1557.seo at samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon at kernel.org>
(backported from commit d42334578eba1390859012ebb91e1e556d51db49)
[yuxuan.luo: manually backported]
CVE-2023-4273
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 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 3940a56902dd..2080eb92f0a9 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;
 	}
 
@@ -1035,7 +1039,8 @@ 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