[PATCH 7.0 07/42] ksmbd: validate owner of durable handle on reconnect

Greg Kroah-Hartman
2026-04-24T13:32:54Z

From: Namjae Jeon <linkinjeon@kernel.org>

[ Upstream commit 49110a8ce654bbe56bef7c5e44cce31f4b102b8a ]

Currently, ksmbd does not verify if the user attempting to reconnect
to a durable handle is the same user who originally opened the file.
This allows any authenticated user to hijack an orphaned durable handle
by predicting or brute-forcing the persistent ID.

According to MS-SMB2, the server MUST verify that the SecurityContext
of the reconnect request matches the SecurityContext associated with
the existing open.
Add a durable_owner structure to ksmbd_file to store the original opener's
UID, GID, and account name. and catpure the owner information when a file
handle becomes orphaned. and implementing ksmbd_vfs_compare_durable_owner()
to validate the identity of the requester during SMB2_CREATE (DHnC).

Fixes: c8efcc786146 ("ksmbd: add support for durable handles v1/v2")
Reported-by: Davide Ornaghi <d.ornaghi97@gmail.com>
Reported-by: Navaneeth K <knavaneeth786@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/mgmt/user_session.c | 8 +--
fs/smb/server/oplock.c | 7 +++
fs/smb/server/oplock.h | 1
fs/smb/server/smb2pdu.c | 3 -
fs/smb/server/vfs_cache.c | 87 ++++++++++++++++++++++++++++++++++----
fs/smb/server/vfs_cache.h | 12 ++++-
6 files changed, 102 insertions(+), 16 deletions(-)

--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -382,12 +382,10 @@ void ksmbd_session_destroy(struct ksmbd_
return;

delete_proc_session(sess);
-
+ ksmbd_tree_conn_session_logoff(sess);
+ ksmbd_destroy_file_table(sess);
if (sess->user)
ksmbd_free_user(sess->user);
-
- ksmbd_tree_conn_session_logoff(sess);
- ksmbd_destroy_file_table(&sess->file_table);
ksmbd_launch_ksmbd_durable_scavenger();
ksmbd_session_rpc_clear_list(sess);
free_channel_list(sess);
@@ -618,7 +616,7 @@ void destroy_previous_session(struct ksm
goto out;
}

- ksmbd_destroy_file_table(&prev_sess->file_table);
+ ksmbd_destroy_file_table(prev_sess);
prev_sess->state = SMB2_SESSION_EXPIRED;
ksmbd_all_conn_set_status(id, KSMBD_SESS_NEED_SETUP);
ksmbd_launch_ksmbd_durable_scavenger();
--- a/fs/smb/server/oplock.c
+++ b/fs/smb/server/oplock.c
@@ -1841,6 +1841,7 @@ int smb2_check_durable_oplock(struct ksm
struct ksmbd_share_config *share,
struct ksmbd_file *fp,
struct lease_ctx_info *lctx,
+ struct ksmbd_user *user,
char *name)
{
struct oplock_info *opinfo = opinfo_get(fp);
@@ -1849,6 +1850,12 @@ int smb2_check_durable_oplock(struct ksm
if (!opinfo)
return 0;

+ if (ksmbd_vfs_compare_durable_owner(fp, user) == false) {
+ ksmbd_debug(SMB, "Durable handle reconnect failed: owner mismatch\n");
+ ret = -EBADF;
+ goto out;
+ }
+
if (opinfo->is_lease == false) {
if (lctx) {
pr_err("create context include lease\n");
--- a/fs/smb/server/oplock.h
+++ b/fs/smb/server/oplock.h
@@ -126,5 +126,6 @@ int smb2_check_durable_oplock(struct ksm
struct ksmbd_share_config *share,
struct ksmbd_file *fp,
struct lease_ctx_info *lctx,
+ struct ksmbd_user *user,
char *name);
#endif /* __KSMBD_OPLOCK_H */
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -3013,7 +3013,8 @@ int smb2_open(struct ksmbd_work *work)
}

if (dh_info.reconnected == true) {
- rc = smb2_check_durable_oplock(conn, share, dh_info.fp, lc, name);
+ rc = smb2_check_durable_oplock(conn, share, dh_info.fp,
+ lc, sess->user, name);
if (rc) {
ksmbd_put_durable_fd(dh_info.fp);
goto err_out2;
--- a/fs/smb/server/vfs_cache.c
+++ b/fs/smb/server/vfs_cache.c
@@ -19,6 +19,7 @@
#include "misc.h"
#include "mgmt/tree_connect.h"
#include "mgmt/user_session.h"
+#include "mgmt/user_config.h"
#include "smb_common.h"
#include "server.h"
#include "smb2pdu.h"
@@ -476,6 +477,8 @@ static void __ksmbd_close_fd(struct ksmb

if (ksmbd_stream_fd(fp))
kfree(fp->stream.name);
+ kfree(fp->owner.name);
+
kmem_cache_free(filp_cache, fp);
}

@@ -787,11 +790,13 @@ void ksmbd_update_fstate(struct ksmbd_fi
}

static int
-__close_file_table_ids(struct ksmbd_file_table *ft,
+__close_file_table_ids(struct ksmbd_session *sess,
struct ksmbd_tree_connect *tcon,
bool (*skip)(struct ksmbd_tree_connect *tcon,
- struct ksmbd_file *fp))
+ struct ksmbd_file *fp,
+ struct ksmbd_user *user))
{
+ struct ksmbd_file_table *ft = &sess->file_table;
struct ksmbd_file *fp;
unsigned int id = 0;
int num = 0;
@@ -804,7 +809,7 @@ __close_file_table_ids(struct ksmbd_file
break;
}

- if (skip(tcon, fp) ||
+ if (skip(tcon, fp, sess->user) ||
!atomic_dec_and_test(&fp->refcount)) {
id++;
write_unlock(&ft->lock);
@@ -856,7 +861,8 @@ static inline bool is_reconnectable(stru
}

static bool tree_conn_fd_check(struct ksmbd_tree_connect *tcon,
- struct ksmbd_file *fp)
+ struct ksmbd_file *fp,
+ struct ksmbd_user *user)
{
return fp->tcon != tcon;
}
@@ -991,8 +997,62 @@ void ksmbd_stop_durable_scavenger(void)
kthread_stop(server_conf.dh_task);
}

+/*
+ * ksmbd_vfs_copy_durable_owner - Copy owner info for durable reconnect
+ * @fp: ksmbd file pointer to store owner info
+ * @user: user pointer to copy from
+ *
+ * This function binds the current user's identity to the file handle
+ * to satisfy MS-SMB2 Step 8 (SecurityContext matching) during reconnect.
+ *
+ * Return: 0 on success, or negative error code on failure
+ */
+static int ksmbd_vfs_copy_durable_owner(struct ksmbd_file *fp,
+ struct ksmbd_user *user)
+{
+ if (!user)
+ return -EINVAL;
+
+ /* Duplicate the user name to ensure identity persistence */
+ fp->owner.name = kstrdup(user->name, GFP_KERNEL);
+ if (!fp->owner.name)
+ return -ENOMEM;
+
+ fp->owner.uid = user->uid;
+ fp->owner.gid = user->gid;
+
+ return 0;
+}
+
+/**
+ * ksmbd_vfs_compare_durable_owner - Verify if the requester is original owner
+ * @fp: existing ksmbd file pointer
+ * @user: user pointer of the reconnect requester
+ *
+ * Compares the UID, GID, and name of the current requester against the
+ * original owner stored in the file handle.
+ *
+ * Return: true if the user matches, false otherwise
+ */
+bool ksmbd_vfs_compare_durable_owner(struct ksmbd_file *fp,
+ struct ksmbd_user *user)
+{
+ if (!user || !fp->owner.name)
+ return false;
+
+ /* Check if the UID and GID match first (fast path) */
+ if (fp->owner.uid != user->uid || fp->owner.gid != user->gid)
+ return false;
+
+ /* Validate the account name to ensure the same SecurityContext */
+ if (strcmp(fp->owner.name, user->name))
+ return false;
+
+ return true;
+}
+
static bool session_fd_check(struct ksmbd_tree_connect *tcon,
- struct ksmbd_file *fp)
+ struct ksmbd_file *fp, struct ksmbd_user *user)
{
struct ksmbd_inode *ci;
struct oplock_info *op;
@@ -1002,6 +1062,9 @@ static bool session_fd_check(struct ksmb
if (!is_reconnectable(fp))
return false;

+ if (ksmbd_vfs_copy_durable_owner(fp, user))
+ return false;
+
conn = fp->conn;
ci = fp->f_ci;
down_write(&ci->m_lock);
@@ -1033,7 +1096,7 @@ static bool session_fd_check(struct ksmb

void ksmbd_close_tree_conn_fds(struct ksmbd_work *work)
{
- int num = __close_file_table_ids(&work->sess->file_table,
+ int num = __close_file_table_ids(work->sess,
work->tcon,
tree_conn_fd_check);

@@ -1042,7 +1105,7 @@ void ksmbd_close_tree_conn_fds(struct ks

void ksmbd_close_session_fds(struct ksmbd_work *work)
{
- int num = __close_file_table_ids(&work->sess->file_table,
+ int num = __close_file_table_ids(work->sess,
work->tcon,
session_fd_check);

@@ -1140,6 +1203,10 @@ int ksmbd_reopen_durable_fd(struct ksmbd
}
up_write(&ci->m_lock);

+ fp->owner.uid = fp->owner.gid = 0;
+ kfree(fp->owner.name);
+ fp->owner.name = NULL;
+
return 0;
}

@@ -1154,12 +1221,14 @@ int ksmbd_init_file_table(struct ksmbd_f
return 0;
}

-void ksmbd_destroy_file_table(struct ksmbd_file_table *ft)
+void ksmbd_destroy_file_table(struct ksmbd_session *sess)
{
+ struct ksmbd_file_table *ft = &sess->file_table;
+
if (!ft->idr)
return;

- __close_file_table_ids(ft, NULL, session_fd_check);
+ __close_file_table_ids(sess, NULL, session_fd_check);
idr_destroy(ft->idr);
kfree(ft->idr);
ft->idr = NULL;
--- a/fs/smb/server/vfs_cache.h
+++ b/fs/smb/server/vfs_cache.h
@@ -68,6 +68,13 @@ enum {
FP_CLOSED
};

+/* Owner information for durable handle reconnect */
+struct durable_owner {
+ unsigned int uid;
+ unsigned int gid;
+ char *name;
+};
+
struct ksmbd_file {
struct file *filp;
u64 persistent_id;
@@ -114,6 +121,7 @@ struct ksmbd_file {
bool is_resilient;

bool is_posix_ctxt;
+ struct durable_owner owner;
};

static inline void set_ctx_actor(struct dir_context *ctx,
@@ -140,7 +148,7 @@ static inline bool ksmbd_stream_fd(struc
}

int ksmbd_init_file_table(struct ksmbd_file_table *ft);
-void ksmbd_destroy_file_table(struct ksmbd_file_table *ft);
+void ksmbd_destroy_file_table(struct ksmbd_session *sess);
int ksmbd_close_fd(struct ksmbd_work *work, u64 id);
struct ksmbd_file *ksmbd_lookup_fd_fast(struct ksmbd_work *work, u64 id);
struct ksmbd_file *ksmbd_lookup_foreign_fd(struct ksmbd_work *work, u64 id);
@@ -166,6 +174,8 @@ void ksmbd_free_global_file_table(void);
void ksmbd_set_fd_limit(unsigned long limit);
void ksmbd_update_fstate(struct ksmbd_file_table *ft, struct ksmbd_file *fp,
unsigned int state);
+bool ksmbd_vfs_compare_durable_owner(struct ksmbd_file *fp,
+ struct ksmbd_user *user);

/*
* INODE hash