FAILED: patch "[PATCH] configfs: pin the symlink target's dirent instead of chasing" failed to apply to 6.12-stable tree

FAILED: patch "[PATCH] configfs: pin the symlink target's dirent instead of chasing" failed to apply to 6.12-stable tree

[gregkh]

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 <stable@vger.kernel.org>.

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 a7c1290eef60711c10289c056ad32ed1f2b47b12
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026091642-reroute-scrap-0bef@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

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

From a7c1290eef60711c10289c056ad32ed1f2b47b12 Mon Sep 17 00:00:00 2001
From: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Date: Thu, 30 Jul 2026 11:30:24 +0200
Subject: [PATCH] configfs: pin the symlink target's dirent instead of chasing
 ->ci_dentry

create_link() reads the target's configfs_dirent from
item->ci_dentry->d_fsdata, relying on the item reference taken by
get_target().  That reference pins the item, not its dentry: the dentry is
pinned by DCACHE_PERSISTENT, which configfs_remove_dir() releases via
simple_rmdir() while the item is still alive.  A symlink racing with rmdir
of its target can therefore find ->ci_dentry freed and its dirent
released, triggering WARN_ON(!atomic_read(&sd->s_count)) in configfs_get().

Take the dirent in get_target() as well, under ->d_lock and atomically
with the item reference, and pass it down to create_link().  A hashed
dentry has not been killed yet, so its ->d_fsdata reference keeps the
dirent alive there.

Cc: stable@vger.kernel.org
Fixes: 7063fbf22611 ("[PATCH] configfs: User-driven configuration filesystem")
Signed-off-by: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Tested-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260730093435.195441-2-vasilisalmpanis@gmail.com
Signed-off-by: Breno Leitao <leitao@debian.org>

diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index 31eb28b27309..3b31c714400f 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -76,9 +76,9 @@ static int configfs_get_target_path(struct config_item *item,
 
 static int create_link(struct config_item *parent_item,
 		       struct config_item *item,
+		       struct configfs_dirent *target_sd,
 		       struct dentry *dentry)
 {
-	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
 	char *body;
 	int ret;
 
@@ -115,6 +115,7 @@ static int create_link(struct config_item *parent_item,
 
 
 static int get_target(const char *symname, struct config_item **target,
+		      struct configfs_dirent **target_sd,
 		      struct super_block *sb)
 {
 	struct path path __free(path_put) = {};
@@ -125,7 +126,20 @@ static int get_target(const char *symname, struct config_item **target,
 		return ret;
 	if (path.dentry->d_sb != sb)
 		return -EPERM;
-	*target = configfs_get_config_item(path.dentry);
+	/*
+	 * A hashed dentry guarantees that neither the item nor the dirent
+	 * have been released yet, as removals unhash before dropping.
+	 * Grab both references here. An item reference alone would not keep
+	 * ->ci_dentry alive.
+	 */
+	spin_lock(&path.dentry->d_lock);
+	if (!d_unhashed(path.dentry)) {
+		struct configfs_dirent *sd = path.dentry->d_fsdata;
+
+		*target = config_item_get(sd->s_element);
+		*target_sd = configfs_get(sd);
+	}
+	spin_unlock(&path.dentry->d_lock);
 	if (!*target)
 		return -ENOENT;
 	return 0;
@@ -139,6 +153,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	struct configfs_dirent *sd;
 	struct config_item *parent_item;
 	struct config_item *target_item = NULL;
+	struct configfs_dirent *target_sd = NULL;
 	const struct config_item_type *type;
 
 	sd = dentry->d_parent->d_fsdata;
@@ -182,7 +197,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	 *  AV, a thoroughly annoyed bastard.
 	 */
 	inode_unlock(dir);
-	ret = get_target(symname, &target_item, dentry->d_sb);
+	ret = get_target(symname, &target_item, &target_sd, dentry->d_sb);
 	inode_lock(dir);
 	if (ret)
 		goto out_put;
@@ -196,13 +211,14 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 		ret = type->ct_item_ops->allow_link(parent_item, target_item);
 	if (!ret) {
 		mutex_lock(&configfs_symlink_mutex);
-		ret = create_link(parent_item, target_item, dentry);
+		ret = create_link(parent_item, target_item, target_sd, dentry);
 		mutex_unlock(&configfs_symlink_mutex);
 		if (ret && type->ct_item_ops->drop_link)
 			type->ct_item_ops->drop_link(parent_item,
 						     target_item);
 	}
 
+	configfs_put(target_sd);
 	config_item_put(target_item);
 
 out_put:

[PATCH 6.12.y 1/2] configfs:get_target() - release path as soon as we grab configfs_item reference

[Sasha Levin]

From: Al Viro <viro@zeniv.linux.org.uk>

[ Upstream commit 1b25dea3867abc9bad6f0337d395c6f0ce4e4f6f ]

... and get rid of path argument - it turns into a local variable in get_target()

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Stable-dep-of: a7c1290eef60 ("configfs: pin the symlink target's dirent instead of chasing ->ci_dentry")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/configfs/symlink.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index 69133ec1fac2a..f3f79c67add5d 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -114,26 +114,21 @@ static int create_link(struct config_item *parent_item,
 }
 
 
-static int get_target(const char *symname, struct path *path,
-		      struct config_item **target, struct super_block *sb)
+static int get_target(const char *symname, struct config_item **target,
+		      struct super_block *sb)
 {
+	struct path path __free(path_put) = {};
 	int ret;
 
-	ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
-	if (!ret) {
-		if (path->dentry->d_sb == sb) {
-			*target = configfs_get_config_item(path->dentry);
-			if (!*target) {
-				ret = -ENOENT;
-				path_put(path);
-			}
-		} else {
-			ret = -EPERM;
-			path_put(path);
-		}
-	}
-
-	return ret;
+	ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, &path);
+	if (ret)
+		return ret;
+	if (path.dentry->d_sb != sb)
+		return -EPERM;
+	*target = configfs_get_config_item(path.dentry);
+	if (!*target)
+		return -ENOENT;
+	return 0;
 }
 
 
@@ -141,7 +136,6 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 		     struct dentry *dentry, const char *symname)
 {
 	int ret;
-	struct path path;
 	struct configfs_dirent *sd;
 	struct config_item *parent_item;
 	struct config_item *target_item = NULL;
@@ -188,7 +182,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	 *  AV, a thoroughly annoyed bastard.
 	 */
 	inode_unlock(dir);
-	ret = get_target(symname, &path, &target_item, dentry->d_sb);
+	ret = get_target(symname, &target_item, dentry->d_sb);
 	inode_lock(dir);
 	if (ret)
 		goto out_put;
@@ -210,7 +204,6 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	}
 
 	config_item_put(target_item);
-	path_put(&path);
 
 out_put:
 	config_item_put(parent_item);
-- 
2.53.0

[PATCH 6.12.y 2/2] configfs: pin the symlink target's dirent instead of chasing ->ci_dentry

[Sasha Levin]

From: Vasileios Almpanis <vasilisalmpanis@gmail.com>

[ Upstream commit a7c1290eef60711c10289c056ad32ed1f2b47b12 ]

create_link() reads the target's configfs_dirent from
item->ci_dentry->d_fsdata, relying on the item reference taken by
get_target().  That reference pins the item, not its dentry: the dentry is
pinned by DCACHE_PERSISTENT, which configfs_remove_dir() releases via
simple_rmdir() while the item is still alive.  A symlink racing with rmdir
of its target can therefore find ->ci_dentry freed and its dirent
released, triggering WARN_ON(!atomic_read(&sd->s_count)) in configfs_get().

Take the dirent in get_target() as well, under ->d_lock and atomically
with the item reference, and pass it down to create_link().  A hashed
dentry has not been killed yet, so its ->d_fsdata reference keeps the
dirent alive there.

Cc: stable@vger.kernel.org
Fixes: 7063fbf22611 ("[PATCH] configfs: User-driven configuration filesystem")
Signed-off-by: Vasileios Almpanis <vasilisalmpanis@gmail.com>
Tested-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260730093435.195441-2-vasilisalmpanis@gmail.com
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/configfs/symlink.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
index f3f79c67add5d..b42f07e2ea7f5 100644
--- a/fs/configfs/symlink.c
+++ b/fs/configfs/symlink.c
@@ -76,9 +76,9 @@ static int configfs_get_target_path(struct config_item *item,
 
 static int create_link(struct config_item *parent_item,
 		       struct config_item *item,
+		       struct configfs_dirent *target_sd,
 		       struct dentry *dentry)
 {
-	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
 	char *body;
 	int ret;
 
@@ -115,6 +115,7 @@ static int create_link(struct config_item *parent_item,
 
 
 static int get_target(const char *symname, struct config_item **target,
+		      struct configfs_dirent **target_sd,
 		      struct super_block *sb)
 {
 	struct path path __free(path_put) = {};
@@ -125,7 +126,20 @@ static int get_target(const char *symname, struct config_item **target,
 		return ret;
 	if (path.dentry->d_sb != sb)
 		return -EPERM;
-	*target = configfs_get_config_item(path.dentry);
+	/*
+	 * A hashed dentry guarantees that neither the item nor the dirent
+	 * have been released yet, as removals unhash before dropping.
+	 * Grab both references here. An item reference alone would not keep
+	 * ->ci_dentry alive.
+	 */
+	spin_lock(&path.dentry->d_lock);
+	if (!d_unhashed(path.dentry)) {
+		struct configfs_dirent *sd = path.dentry->d_fsdata;
+
+		*target = config_item_get(sd->s_element);
+		*target_sd = configfs_get(sd);
+	}
+	spin_unlock(&path.dentry->d_lock);
 	if (!*target)
 		return -ENOENT;
 	return 0;
@@ -139,6 +153,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	struct configfs_dirent *sd;
 	struct config_item *parent_item;
 	struct config_item *target_item = NULL;
+	struct configfs_dirent *target_sd = NULL;
 	const struct config_item_type *type;
 
 	sd = dentry->d_parent->d_fsdata;
@@ -182,7 +197,7 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 	 *  AV, a thoroughly annoyed bastard.
 	 */
 	inode_unlock(dir);
-	ret = get_target(symname, &target_item, dentry->d_sb);
+	ret = get_target(symname, &target_item, &target_sd, dentry->d_sb);
 	inode_lock(dir);
 	if (ret)
 		goto out_put;
@@ -196,13 +211,14 @@ int configfs_symlink(struct mnt_idmap *idmap, struct inode *dir,
 		ret = type->ct_item_ops->allow_link(parent_item, target_item);
 	if (!ret) {
 		mutex_lock(&configfs_symlink_mutex);
-		ret = create_link(parent_item, target_item, dentry);
+		ret = create_link(parent_item, target_item, target_sd, dentry);
 		mutex_unlock(&configfs_symlink_mutex);
 		if (ret && type->ct_item_ops->drop_link)
 			type->ct_item_ops->drop_link(parent_item,
 						     target_item);
 	}
 
+	configfs_put(target_sd);
 	config_item_put(target_item);
 
 out_put:
-- 
2.53.0