FAILED: patch "[PATCH] ksmbd: fix session reference leak on compounded SESSION_SETUP" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 03bd8f5279e490e15e0c0f0fa388ffbd2fbacd65
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110317-undermost-pretty-44e0@gregkh' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 03bd8f5279e490e15e0c0f0fa388ffbd2fbacd65 Mon Sep 17 00:00:00 2001
From: Ian Bridges <[email protected]>
Date: Tue, 27 Oct 2026 10:21:35 -0500
Subject: [PATCH] ksmbd: fix session reference leak on compounded SESSION_SETUP

A compound request can place SESSION_SETUP after another command. That earlier command leaves a reference to its session in work->sess. smb2_sess_setup() then overwrites work->sess with the session it looks up or creates, and the dispatcher later puts work->sess only once. The inherited reference is never dropped. That leaks the session, together with its setup connection and socket, and every repeat of the compound leaks another.

unreferenced object (size 512):

    __kmalloc_cache_noprof+0x32c/0x3a0
    ksmbd_smb2_session_create+0xf6/0x9c0 [ksmbd]
    smb2_sess_setup+0xda4/0x6280 [ksmbd]
    handle_ksmbd_work+0x88c/0x1cb0 [ksmbd]

Save the inherited session on entry. After the request has been processed, release it once, but only when smb2_sess_setup() has replaced work->sess with its own session or cleared it. Do this after ksmbd_conn_unlock() so the put does not run under srv_mutex. An error path may instead leave the inherited session in work->sess. Keep it there, so the dispatcher still puts it and the error response is still signed or encrypted with it as before.

index f4b61521beac..9f2b435fd437 100644
@@ -2563,6 +2563,8 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	struct smb2_sess_setup_req *req;
 	struct smb2_sess_setup_rsp *rsp;
 	struct ksmbd_session *sess = NULL;
+	struct ksmbd_session *prev_sess = work->sess;
+	bool installed = false;
 	struct negotiate_message *negblob;
 	unsigned int negblob_len, negblob_off;
 	u64 previous_session_id = 0;

@@ -2679,6 +2681,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			int sign_ret;
 
 			work->sess = sess;
+			installed = true;
 			if (sess->dialect >= SMB30_PROT_ID)
 				sign_ret = smb3_check_sign_req(work);
 			else

@@ -2731,6 +2734,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 		conn->binding = false;
 	}
 	work->sess = sess;
+	installed = true;
 
 	negblob_off = le16_to_cpu(req->SecurityBufferOffset);
 	negblob_len = le16_to_cpu(req->SecurityBufferLength);

@@ -2928,6 +2932,14 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	}
 
 	ksmbd_conn_unlock(conn);
+
+	/*
+	 * Later in a compound, work->sess holds the reference that an
+	 * earlier command took. Drop it once this request has installed
+	 * its own session there or cleared it.
+	 */
+	if (prev_sess && (installed || !work->sess))
+		ksmbd_user_session_put(prev_sess);
 	return rc;
 }
 

From: Ian Bridges <[email protected]>

[ Upstream commit 03bd8f5279e490e15e0c0f0fa388ffbd2fbacd65 ]

A compound request can place SESSION_SETUP after another command. That earlier command leaves a reference to its session in work->sess. smb2_sess_setup() then overwrites work->sess with the session it looks up or creates, and the dispatcher later puts work->sess only once. The inherited reference is never dropped. That leaks the session, together with its setup connection and socket, and every repeat of the compound leaks another.

unreferenced object (size 512):

    __kmalloc_cache_noprof+0x32c/0x3a0
    ksmbd_smb2_session_create+0xf6/0x9c0 [ksmbd]
    smb2_sess_setup+0xda4/0x6280 [ksmbd]
    handle_ksmbd_work+0x88c/0x1cb0 [ksmbd]

Save the inherited session on entry. After the request has been processed, release it once, but only when smb2_sess_setup() has replaced work->sess with its own session or cleared it. Do this after ksmbd_conn_unlock() so the put does not run under srv_mutex. An error path may instead leave the inherited session in work->sess. Keep it there, so the dispatcher still puts it and the error response is still signed or encrypted with it as before.

---
 fs/smb/server/smb2pdu.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

index 793c219b9a610..7c4b41a523e7a 100644
@@ -1698,6 +1698,8 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	struct smb2_sess_setup_req *req;
 	struct smb2_sess_setup_rsp *rsp;
 	struct ksmbd_session *sess;
+	struct ksmbd_session *prev_sess = work->sess;
+	bool installed = false;
 	struct negotiate_message *negblob;
 	unsigned int negblob_len, negblob_off;
 	int rc = 0;

@@ -1835,6 +1837,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 		conn->binding = false;
 	}
 	work->sess = sess;
+	installed = true;
 
 	negblob_off = le16_to_cpu(req->SecurityBufferOffset);
 	negblob_len = le16_to_cpu(req->SecurityBufferLength);

@@ -1988,6 +1991,14 @@ int smb2_sess_setup(struct ksmbd_work *work)
 	}
 
 	ksmbd_conn_unlock(conn);
+
+	/*
+	 * Later in a compound, work->sess holds the reference that an
+	 * earlier command took. Drop it once this request has installed
+	 * its own session there or cleared it.
+	 */
+	if (prev_sess && (installed || !work->sess))
+		ksmbd_user_session_put(prev_sess);
 	return rc;
 }
 

2.53.0