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) <[e-mail]>
Cc: [e-mail] # 6.2
Signed-off-by: Steve French <[e-mail]>

fs/cifs/cifs_fs_sb.h

···
 	/* only used when CIFS_MOUNT_USE_PREFIX_PATH is set */
 	char *prepath;
 
-	/* randomly generated 128-bit number for indexing dfs mount groups in referral cache */
-	uuid_t dfs_mount_id;
 	/*
 	 * Indicate whether serverino option was turned off later
 	 * (cifs_autodisable_serverino) in order to match new mounts.

fs/cifs/cifsglob.h

···
 	/* BB add field for back pointer to sb struct(s)? */
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	struct list_head ulist; /* cache update list */
+	struct list_head dfs_ses_list;
 #endif
 	struct delayed_work	query_interfaces; /* query interfaces workqueue job */
 };
···
 	struct TCP_Server_Info *server;
 	struct cifs_ses *ses;
 	struct cifs_tcon *tcon;
-	uuid_t mount_id;
 	char *origin_fullpath, *leaf_fullpath;
+	struct list_head dfs_ses_list;
 };
 
 static inline void free_dfs_info_param(struct dfs_info3_param *param)

fs/cifs/connect.c

···
 	bool isdfs;
 	int rc;
 
-	uuid_gen(&mnt_ctx.mount_id);
+	INIT_LIST_HEAD(&mnt_ctx.dfs_ses_list);
+
 	rc = dfs_mount_share(&mnt_ctx, &isdfs);
 	if (rc)
 		goto error;
···
 	kfree(cifs_sb->prepath);
 	cifs_sb->prepath = ctx->prepath;
 	ctx->prepath = NULL;
-	uuid_copy(&cifs_sb->dfs_mount_id, &mnt_ctx.mount_id);
 
 out:
 	cifs_try_adding_channels(cifs_sb, mnt_ctx.ses);
···
 	return rc;
 
 error:
-	dfs_cache_put_refsrv_sessions(&mnt_ctx.mount_id);
+	dfs_put_root_smb_sessions(&mnt_ctx.dfs_ses_list);
 	kfree(mnt_ctx.origin_fullpath);
 	kfree(mnt_ctx.leaf_fullpath);
 	cifs_mount_put_conns(&mnt_ctx);
···
 	spin_unlock(&cifs_sb->tlink_tree_lock);
 
 	kfree(cifs_sb->prepath);
-#ifdef CONFIG_CIFS_DFS_UPCALL
-	dfs_cache_put_refsrv_sessions(&cifs_sb->dfs_mount_id);
-#endif
 	call_rcu(&cifs_sb->rcu, delayed_free);
 }
 

fs/cifs/dfs.c

···
 	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,
···
 {
 	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)
···
 	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) {
···
 			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:
···
 	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;
···
 
 	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:
···
 	}
 
 	*isdfs = true;
-	set_root_ses(mnt_ctx);
+	rc = get_root_smb_session(mnt_ctx);
+	if (rc)
+		return rc;
 
 	return __dfs_mount_share(mnt_ctx);
 }

fs/cifs/dfs.h

···
 #include "fs_context.h"
 #include "cifs_unicode.h"
 
+struct dfs_root_ses {
+	struct list_head list;
+	struct cifs_ses *ses;
+};
+
 int dfs_parse_target_referral(const char *full_path, const struct dfs_info3_param *ref,
 			      struct smb3_fs_context *ctx);
 int dfs_mount_share(struct cifs_mount_ctx *mnt_ctx, bool *isdfs);
···
 							server->origin_fullpath,
 							strlen(server->origin_fullpath),
 							true);
+}
+
+static inline void dfs_put_root_smb_sessions(struct list_head *head)
+{
+	struct dfs_root_ses *root, *tmp;
+
+	list_for_each_entry_safe(root, tmp, head, list) {
+		list_del_init(&root->list);
+		cifs_put_smb_ses(root->ses);
+		kfree(root);
+	}
 }
 
 #endif /* _CIFS_DFS_H */

fs/cifs/dfs_cache.c

···
 	struct cache_dfs_tgt *tgthint;
 };
 
-/* List of referral server sessions per dfs mount */
-struct mount_group {
-	struct list_head list;
-	uuid_t id;
-	struct cifs_ses *sessions[CACHE_MAX_ENTRIES];
-	int num_sessions;
-	spinlock_t lock;
-	struct list_head refresh_list;
-	struct kref refcount;
-};
-
 static struct kmem_cache *cache_slab __read_mostly;
 static struct workqueue_struct *dfscache_wq __read_mostly;
 
···
 static struct hlist_head cache_htable[CACHE_HTABLE_SIZE];
 static DECLARE_RWSEM(htable_rw_lock);
 
-static LIST_HEAD(mount_group_list);
-static DEFINE_MUTEX(mount_group_list_lock);
-
 static void refresh_cache_worker(struct work_struct *work);
 
 static DECLARE_DELAYED_WORK(refresh_task, refresh_cache_worker);
-
-static void __mount_group_release(struct mount_group *mg)
-{
-	int i;
-
-	for (i = 0; i < mg->num_sessions; i++)
-		cifs_put_smb_ses(mg->sessions[i]);
-	kfree(mg);
-}
-
-static void mount_group_release(struct kref *kref)
-{
-	struct mount_group *mg = container_of(kref, struct mount_group, refcount);
-
-	mutex_lock(&mount_group_list_lock);
-	list_del(&mg->list);
-	mutex_unlock(&mount_group_list_lock);
-	__mount_group_release(mg);
-}
-
-static struct mount_group *find_mount_group_locked(const uuid_t *id)
-{
-	struct mount_group *mg;
-
-	list_for_each_entry(mg, &mount_group_list, list) {
-		if (uuid_equal(&mg->id, id))
-			return mg;
-	}
-	return ERR_PTR(-ENOENT);
-}
-
-static struct mount_group *__get_mount_group_locked(const uuid_t *id)
-{
-	struct mount_group *mg;
-
-	mg = find_mount_group_locked(id);
-	if (!IS_ERR(mg))
-		return mg;
-
-	mg = kmalloc(sizeof(*mg), GFP_KERNEL);
-	if (!mg)
-		return ERR_PTR(-ENOMEM);
-	kref_init(&mg->refcount);
-	uuid_copy(&mg->id, id);
-	mg->num_sessions = 0;
-	spin_lock_init(&mg->lock);
-	list_add(&mg->list, &mount_group_list);
-	return mg;
-}
-
-static struct mount_group *get_mount_group(const uuid_t *id)
-{
-	struct mount_group *mg;
-
-	mutex_lock(&mount_group_list_lock);
-	mg = __get_mount_group_locked(id);
-	if (!IS_ERR(mg))
-		kref_get(&mg->refcount);
-	mutex_unlock(&mount_group_list_lock);
-
-	return mg;
-}
-
-static void free_mount_group_list(void)
-{
-	struct mount_group *mg, *tmp_mg;
-
-	list_for_each_entry_safe(mg, tmp_mg, &mount_group_list, list) {
-		list_del_init(&mg->list);
-		__mount_group_release(mg);
-	}
-}
 
 /**
  * dfs_cache_canonical_path - get a canonical DFS path
···
 {
 	cancel_delayed_work_sync(&refresh_task);
 	unload_nls(cache_cp);
-	free_mount_group_list();
 	flush_cache_ents();
 	kmem_cache_destroy(cache_slab);
 	destroy_workqueue(dfscache_wq);
···
 	return rc;
 }
 
-/**
- * dfs_cache_add_refsrv_session - add SMB session of referral server
- *
- * @mount_id: mount group uuid to lookup.
- * @ses: reference counted SMB session of referral server.
- */
-void dfs_cache_add_refsrv_session(const uuid_t *mount_id, struct cifs_ses *ses)
-{
-	struct mount_group *mg;
-
-	if (WARN_ON_ONCE(!mount_id || uuid_is_null(mount_id) || !ses))
-		return;
-
-	mg = get_mount_group(mount_id);
-	if (WARN_ON_ONCE(IS_ERR(mg)))
-		return;
-
-	spin_lock(&mg->lock);
-	if (mg->num_sessions < ARRAY_SIZE(mg->sessions))
-		mg->sessions[mg->num_sessions++] = ses;
-	spin_unlock(&mg->lock);
-	kref_put(&mg->refcount, mount_group_release);
-}
-
-/**
- * dfs_cache_put_refsrv_sessions - put all referral server sessions
- *
- * Put all SMB sessions from the given mount group id.
- *
- * @mount_id: mount group uuid to lookup.
- */
-void dfs_cache_put_refsrv_sessions(const uuid_t *mount_id)
-{
-	struct mount_group *mg;
-
-	if (!mount_id || uuid_is_null(mount_id))
-		return;
-
-	mutex_lock(&mount_group_list_lock);
-	mg = find_mount_group_locked(mount_id);
-	if (IS_ERR(mg)) {
-		mutex_unlock(&mount_group_list_lock);
-		return;
-	}
-	mutex_unlock(&mount_group_list_lock);
-	kref_put(&mg->refcount, mount_group_release);
-}
-
 /* Extract share from DFS target and return a pointer to prefix path or NULL */
 static const char *parse_target_share(const char *target, char **share)
 {
···
 	if (!server->origin_fullpath) {
 		cifs_dbg(FYI, "%s: not a dfs mount\n", __func__);
 		return 0;
-	}
-
-	if (uuid_is_null(&cifs_sb->dfs_mount_id)) {
-		cifs_dbg(FYI, "%s: no dfs mount group id\n", __func__);
-		return -EINVAL;
 	}
 	/*
 	 * After reconnecting to a different server, unique ids won't match anymore, so we disable

fs/cifs/dfs_cache.h

···
 			       struct dfs_info3_param *ref);
 int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it, char **share,
 			    char **prefix);
-void dfs_cache_put_refsrv_sessions(const uuid_t *mount_id);
-void dfs_cache_add_refsrv_session(const uuid_t *mount_id, struct cifs_ses *ses);
 char *dfs_cache_canonical_path(const char *path, const struct nls_table *cp, int remap);
 int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb);
 

fs/cifs/misc.c

···
 #ifdef CONFIG_CIFS_DFS_UPCALL
 #include "dns_resolve.h"
 #include "dfs_cache.h"
+#include "dfs.h"
 #endif
 #include "fs_context.h"
 #include "cached_dir.h"
···
 	spin_lock_init(&ret_buf->stat_lock);
 	atomic_set(&ret_buf->num_local_opens, 0);
 	atomic_set(&ret_buf->num_remote_opens, 0);
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	INIT_LIST_HEAD(&ret_buf->dfs_ses_list);
+#endif
 
 	return ret_buf;
 }
···
 	atomic_dec(&tconInfoAllocCount);
 	kfree(tcon->nativeFileSystem);
 	kfree_sensitive(tcon->password);
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	dfs_put_root_smb_sessions(&tcon->dfs_ses_list);
+#endif
 	kfree(tcon);
 }