[PATCH 6.1.y] smb: server: size directory name conversion buffer correctly

[Sasha Levin <sashal@kernel.org>]

From: VeroFess <coderzeng@hotmail.com>

[ Upstream commit f1f37834eaba5904103af1f18afe3510c7e9dc71 ]

A 2048-byte ASCII directory name needs 4098 bytes when converted to
UTF-16, including the terminator. ksmbd_convert_dir_info_name() caps
its allocation at PATH_MAX and writes past the end of that buffer.

Allocate space for one UTF-16 code unit per input byte plus the
terminator. Use kmalloc_array() to check the size calculation.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Assisted-by: gpt 6 sol with daybreak blue
Signed-off-by: VeroFess <coderzeng@hotmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
[ sashal: used GFP_KERNEL instead of KSMBD_DEFAULT_GFP for kmalloc_array() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/misc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/smb/server/misc.c b/fs/smb/server/misc.c
index 98da57bb5fd29..ea6eccbe81bb9 100644
--- a/fs/smb/server/misc.c
+++ b/fs/smb/server/misc.c
@@ -289,12 +289,13 @@ char *ksmbd_convert_dir_info_name(struct ksmbd_dir_info *d_info,
 				  int *conv_len)
 {
 	char *conv;
-	int  sz = min(4 * d_info->name_len, PATH_MAX);
 
-	if (!sz)
+	if (d_info->name_len <= 0)
 		return NULL;
 
-	conv = kmalloc(sz, GFP_KERNEL);
+	/* One UTF-16 code unit per input byte, plus the terminating NUL. */
+	conv = kmalloc_array((size_t)d_info->name_len + 1,
+			     sizeof(__le16), GFP_KERNEL);
 	if (!conv)
 		return NULL;
 
@@ -303,7 +304,6 @@ char *ksmbd_convert_dir_info_name(struct ksmbd_dir_info *d_info,
 				      d_info->name_len, local_nls, 0);
 	*conv_len *= 2;
 
-	/* We allocate buffer twice bigger than needed. */
 	conv[*conv_len] = 0x00;
 	conv[*conv_len + 1] = 0x00;
 	return conv;
-- 
2.53.0