cifs: fix use-after-free bug in refresh_cache_worker()

The UAF bug occurred because we were putting DFS root sessions in
cifs_umount() while DFS cache refresher was being executed.

Make DFS root sessions have same lifetime as DFS tcons so we can avoid
the use-after-free bug is DFS cache refresher and other places that
require IPCs to get new DFS referrals on.  Also, get rid of mount
group handling in DFS cache as we no longer need it.

This fixes below use-after-free bug catched by KASAN

[ 379.946955] BUG: KASAN: use-after-free in __refresh_tcon.isra.0+0x10b/0xc10 [cifs]
[ 379.947642] Read of size 8 at addr ffff888018f57030 by task kworker/u4:3/56
[ 379.948096]
[ 379.948208] CPU: 0 PID: 56 Comm: kworker/u4:3 Not tainted 6.2.0-rc7-lku #23
[ 379.948661] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552-rebuilt.opensuse.org 04/01/2014
[ 379.949368] Workqueue: cifs-dfscache refresh_cache_worker [cifs]
[ 379.949942] Call Trace:
[ 379.950113] <TASK>
[ 379.950260] dump_stack_lvl+0x50/0x67
[ 379.950510] print_report+0x16a/0x48e
[ 379.950759] ? __virt_addr_valid+0xd8/0x160
[ 379.951040] ? __phys_addr+0x41/0x80
[ 379.951285] kasan_report+0xdb/0x110
[ 379.951533] ? __refresh_tcon.isra.0+0x10b/0xc10 [cifs]
[ 379.952056] ? __refresh_tcon.isra.0+0x10b/0xc10 [cifs]
[ 379.952585] __refresh_tcon.isra.0+0x10b/0xc10 [cifs]
[ 379.953096] ? __pfx___refresh_tcon.isra.0+0x10/0x10 [cifs]
[ 379.953637] ? __pfx___mutex_lock+0x10/0x10
[ 379.953915] ? lock_release+0xb6/0x720
[ 379.954167] ? __pfx_lock_acquire+0x10/0x10
[ 379.954443] ? refresh_cache_worker+0x34e/0x6d0 [cifs]
[ 379.954960] ? __pfx_wb_workfn+0x10/0x10
[ 379.955239] refresh_cache_worker+0x4ad/0x6d0 [cifs]
[ 379.955755] ? __pfx_refresh_cache_worker+0x10/0x10 [cifs]
[ 379.956323] ? __pfx_lock_acquired+0x10/0x10
[ 379.956615] ? read_word_at_a_time+0xe/0x20
[ 379.956898] ? lockdep_hardirqs_on_prepare+0x12/0x220
[ 379.957235] process_one_work+0x535/0x990
[ 379.957509] ? __pfx_process_one_work+0x10/0x10
[ 379.957812] ? lock_acquired+0xb7/0x5f0
[ 379.958069] ? __list_add_valid+0x37/0xd0
[ 379.958341] ? __list_add_valid+0x37/0xd0
[ 379.958611] worker_thread+0x8e/0x630
[ 379.958861] ? __pfx_worker_thread+0x10/0x10
[ 379.959148] kthread+0x17d/0x1b0
[ 379.959369] ? __pfx_kthread+0x10/0x10
[ 379.959630] ret_from_fork+0x2c/0x50
[ 379.959879] </TASK>

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Cc: stable@vger.kernel.org # 6.2
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 39 insertions, 13 deletions

diff --git a/fs/cifs/dfs.c b/fs/cifs/dfs.c
index 6505f1b20147..c8bda52fa096 100644
--- a/fs/cifs/dfs.c
+++ b/fs/cifs/dfs.c
@@ -99,18 +99,27 @@ static int get_session(struct cifs_mount_ctx *mnt_ctx, const char *full_path)
 	return rc;
 }
 
-static void set_root_ses(struct cifs_mount_ctx *mnt_ctx)
+static int get_root_smb_session(struct cifs_mount_ctx *mnt_ctx)
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
+	struct dfs_root_ses *root_ses;
 	struct cifs_ses *ses = mnt_ctx->ses;
 
 	if (ses) {
+		root_ses = kmalloc(sizeof(*root_ses), GFP_KERNEL);
+		if (!root_ses)
+			return -ENOMEM;
+
+		INIT_LIST_HEAD(&root_ses->list);
+
 		spin_lock(&cifs_tcp_ses_lock);
 		ses->ses_count++;
 		spin_unlock(&cifs_tcp_ses_lock);
-		dfs_cache_add_refsrv_session(&mnt_ctx->mount_id, ses);
+		root_ses->ses = ses;
+		list_add_tail(&root_ses->list, &mnt_ctx->dfs_ses_list);
 	}
-	ctx->dfs_root_ses = mnt_ctx->ses;
+	ctx->dfs_root_ses = ses;
+	return 0;
 }
 
 static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, const char *full_path,
@@ -118,7 +127,8 @@ static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, co
 {
 	struct smb3_fs_context *ctx = mnt_ctx->fs_ctx;
 	struct dfs_info3_param ref = {};
-	int rc;
+	bool is_refsrv = false;
+	int rc, rc2;
 
 	rc = dfs_cache_get_tgt_referral(ref_path + 1, tit, &ref);
 	if (rc)
@@ -133,8 +143,7 @@ static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, co
 	if (rc)
 		goto out;
 
-	if (ref.flags & DFSREF_REFERRAL_SERVER)
-		set_root_ses(mnt_ctx);
+	is_refsrv = !!(ref.flags & DFSREF_REFERRAL_SERVER);
 
 	rc = -EREMOTE;
 	if (ref.flags & DFSREF_STORAGE_SERVER) {
@@ -143,13 +152,17 @@ static int get_dfs_conn(struct cifs_mount_ctx *mnt_ctx, const char *ref_path, co
 			goto out;
 
 		/* some servers may not advertise referral capability under ref.flags */
-		if (!(ref.flags & DFSREF_REFERRAL_SERVER) &&
-		    is_tcon_dfs(mnt_ctx->tcon))
-			set_root_ses(mnt_ctx);
+		is_refsrv |= is_tcon_dfs(mnt_ctx->tcon);
 
 		rc = cifs_is_path_remote(mnt_ctx);
 	}
 
+	if (rc == -EREMOTE && is_refsrv) {
+		rc2 = get_root_smb_session(mnt_ctx);
+		if (rc2)
+			rc = rc2;
+	}
+
 out:
 	free_dfs_info_param(&ref);
 	return rc;
@@ -162,6 +175,7 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 	char *ref_path = NULL, *full_path = NULL;
 	struct dfs_cache_tgt_iterator *tit;
 	struct TCP_Server_Info *server;
+	struct cifs_tcon *tcon;
 	char *origin_fullpath = NULL;
 	int num_links = 0;
 	int rc;
@@ -231,12 +245,22 @@ static int __dfs_mount_share(struct cifs_mount_ctx *mnt_ctx)
 
 	if (!rc) {
 		server = mnt_ctx->server;
+		tcon = mnt_ctx->tcon;
 
 		mutex_lock(&server->refpath_lock);
-		server->origin_fullpath = origin_fullpath;
-		server->current_fullpath = server->leaf_fullpath;
+		if (!server->origin_fullpath) {
+			server->origin_fullpath = origin_fullpath;
+			server->current_fullpath = server->leaf_fullpath;
+			origin_fullpath = NULL;
+		}
 		mutex_unlock(&server->refpath_lock);
-		origin_fullpath = NULL;
+
+		if (list_empty(&tcon->dfs_ses_list)) {
+			list_replace_init(&mnt_ctx->dfs_ses_list,
+					  &tcon->dfs_ses_list);
+		} else {
+			dfs_put_root_smb_sessions(&mnt_ctx->dfs_ses_list);
+		}
 	}
 
 out:
@@ -277,7 +301,9 @@ int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs)
 	}
 
 	*isdfs = true;
-	set_root_ses(mnt_ctx);
+	rc = get_root_smb_session(mnt_ctx);
+	if (rc)
+		return rc;
 
 	return __dfs_mount_share(mnt_ctx);
 }