[PATCH v2] ksmbd: Replace strcpy + strcat to improve convert_to_nt_pathname

[Thorsten Blum <thorsten.blum@linux.dev>]

strcpy() is deprecated [1] and using strcat() is discouraged. Replace
them by assigning the prefix directly and by using memcpy() to copy the
pathname. Using memcpy() is safe because we already know the length of
the source string and that it is guaranteed to be NUL-terminated.

Allocate only as many bytes as needed and replace kzalloc() with
kmalloc() since memcpy() overwrites the entire buffer anyway.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy [1]
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
Changes in v2:
- Assign the prefix directly if needed
- Use memcpy() instead of scnprintf() (David)
- Allocate only as many bytes as needed
- Replace kzalloc() with kmalloc()
- Update patch title and description
- Link to v1: https://lore.kernel.org/lkml/20251118122555.75624-2-thorsten.blum@linux.dev/
---
 fs/smb/server/misc.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/fs/smb/server/misc.c b/fs/smb/server/misc.c
index cb2a11ffb23f..a543ec9d3581 100644
--- a/fs/smb/server/misc.c
+++ b/fs/smb/server/misc.c
@@ -164,6 +164,8 @@ char *convert_to_nt_pathname(struct ksmbd_share_config *share,
 {
 	char *pathname, *ab_pathname, *nt_pathname;
 	int share_path_len = share->path_sz;
+	size_t ab_pathname_len;
+	int prefix;
 
 	pathname = kmalloc(PATH_MAX, KSMBD_DEFAULT_GFP);
 	if (!pathname)
@@ -180,15 +182,18 @@ char *convert_to_nt_pathname(struct ksmbd_share_config *share,
 		goto free_pathname;
 	}
 
-	nt_pathname = kzalloc(strlen(&ab_pathname[share_path_len]) + 2,
-			      KSMBD_DEFAULT_GFP);
+	ab_pathname_len = strlen(&ab_pathname[share_path_len]);
+	prefix = ab_pathname[share_path_len] == '\0' ? 1 : 0;
+	nt_pathname = kmalloc(prefix + ab_pathname_len + 1, KSMBD_DEFAULT_GFP);
 	if (!nt_pathname) {
 		nt_pathname = ERR_PTR(-ENOMEM);
 		goto free_pathname;
 	}
-	if (ab_pathname[share_path_len] == '\0')
-		strcpy(nt_pathname, "/");
-	strcat(nt_pathname, &ab_pathname[share_path_len]);
+
+	if (prefix)
+		*nt_pathname = '/';
+	memcpy(nt_pathname + prefix, &ab_pathname[share_path_len],
+	       ab_pathname_len + 1);
 
 	ksmbd_conv_path_to_windows(nt_pathname);
 
-- 
2.51.1