FAILED: patch "[PATCH] smb: server: size directory name conversion buffer correctly" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f1f37834eaba5904103af1f18afe3510c7e9dc71
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110425-refining-slum-bcbe@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f1f37834eaba5904103af1f18afe3510c7e9dc71 Mon Sep 17 00:00:00 2001
From: VeroFess <[email protected]>
Date: Mon, 26 Oct 2026 15:01:03 +0900
Subject: [PATCH] smb: server: size directory name conversion buffer correctly

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.

index 2dd91c9e956a..5037f37c9226 100644
@@ -296,12 +296,13 @@ 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, KSMBD_DEFAULT_GFP);
+	/* One UTF-16 code unit per input byte, plus the terminating NUL. */
+	conv = kmalloc_array((size_t)d_info->name_len + 1,
+			     sizeof(__le16), KSMBD_DEFAULT_GFP);
 	if (!conv)
 		return NULL;
 

@@ -310,7 +311,6 @@ 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;

From: VeroFess <[email protected]>

[ 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.

---
 fs/ksmbd/misc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

index 11314f7c622a6..42fa55c0027d6 100644
@@ -322,12 +322,13 @@ 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;
 

@@ -336,7 +337,6 @@ 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