FAILED: patch "[PATCH] ksmbd: prevent share root removal through empty paths" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x 9fd1fcbbf84986a7bcf601a2b90540899069d263
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110337-chute-essential-cb01@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 9fd1fcbbf84986a7bcf601a2b90540899069d263 Mon Sep 17 00:00:00 2001
From: Namjae Jeon <[email protected]>
Date: Fri, 23 Oct 2026 08:53:57 +0900
Subject: [PATCH] ksmbd: prevent share root removal through empty paths

A FileLinkInformation request can supply "/" as the new link name. smb2_get_name() strips the trailing slash and passes an empty string to ksmbd_vfs_kern_path_start_removing().

ksmbd_vfs_path_lookup() resolves an empty pathname as the configured share path, without LOOKUP_BENEATH. With ReplaceIfExists set, smb2_create_link() can therefore remove the share root from its parent before link creation fails. An authenticated client with a writable share and DELETE access to a file can trigger this if the share root is empty and the mapped user has write and search permission on its parent directory.

Return -EINVAL for empty pathnames when for_remove is set, before resolving the share path or acquiring removal resources. Ordinary lookups continue to accept empty pathnames for opening the share root.

index 5360c6999bb3..4ee72eda9bc0 100644
@@ -62,6 +62,10 @@ static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf,
 	struct dentry *d;
 
 	if (pathname[0] == '\0') {
+		/* The share root must never be removed. */
+		if (for_remove)
+			return -EINVAL;
+
 		pathname = share_conf->path;
 		root_share_path = NULL;
 	} else {

From: Namjae Jeon <[email protected]>

[ Upstream commit 9fd1fcbbf84986a7bcf601a2b90540899069d263 ]

A FileLinkInformation request can supply "/" as the new link name. smb2_get_name() strips the trailing slash and passes an empty string to ksmbd_vfs_kern_path_start_removing().

ksmbd_vfs_path_lookup() resolves an empty pathname as the configured share path, without LOOKUP_BENEATH. With ReplaceIfExists set, smb2_create_link() can therefore remove the share root from its parent before link creation fails. An authenticated client with a writable share and DELETE access to a file can trigger this if the share root is empty and the mapped user has write and search permission on its parent directory.

Return -EINVAL for empty pathnames when for_remove is set, before resolving the share path or acquiring removal resources. Ordinary lookups continue to accept empty pathnames for opening the share root.

---
 fs/smb/server/smb2pdu.c | 6 ++++++
 1 file changed, 6 insertions(+)

index 5f752434be3cf..d2330137b9b76 100644
@@ -6339,6 +6339,12 @@ static int smb2_create_link(struct ksmbd_work *work,
 	}
 
 	ksmbd_debug(SMB, "target name is %s\n", target_name);
+	/* The share root must never be removed. */
+	if (link_name[0] == '\0') {
+		rc = -EINVAL;
+		goto out;
+	}
+
 	rc = ksmbd_vfs_kern_path_locked(work, link_name, LOOKUP_NO_SYMLINKS,
 					&parent_path, &path, 0);
 	if (rc) {

2.53.0