[PATCH 7.3.y 2/2] ksmbd: fix use-after-free after a failed durable reconnect

[Sasha Levin <sashal@kernel.org>]

From: Ian Bridges <icb@fastmail.org>

[ Upstream commit 248b5819591c577727930e4e255a455235fab50a ]

ksmbd_reopen_durable_fd() republishes a detached durable handle in the
reconnecting session's file table and takes no reference for that entry.
If smb2_open() then fails, cleanup relies on the final ksmbd_fd_put() to
remove the volatile id.

Two reconnects of the same handle can both take a lookup reference before
either attaches it. If the one that reopens first then fails and drops
its references first, the other request makes the final put through
ksmbd_put_durable_fd(). That frees the handle without removing the first
session's table entry, so tearing that session down writes to freed
memory.

  BUG: KASAN: slab-use-after-free in __close_file_table_ids+0x14d/0x740 [ksmbd]
  Call Trace:
   __close_file_table_ids+0x14d/0x740 [ksmbd]
   ksmbd_destroy_file_table+0x76/0x100 [ksmbd]
   ksmbd_session_destroy+0xf8/0x480 [ksmbd]
   ksmbd_dispose_sessions+0x13e/0x200 [ksmbd]
   ksmbd_conn_sessions_cleanup+0x4c3/0x6d0 [ksmbd]
  Freed by task 1030:
   __ksmbd_close_fd+0x97d/0x1000 [ksmbd]
   smb2_open+0x14eb/0xd9f0 [ksmbd]

Commit 3515503322f4 ("ksmbd: fix durable reconnect error path file
lifetime") handles a final put made by the reconnecting request, but not
one made by another holder.

Remove the volatile id under the file-table lock on this error path,
before the references are dropped, as ksmbd_close_fd() does on the
request_open path just above. Removal then no longer depends on which
holder makes the final put. The stale comment in the reconnect cleanup
is updated to match. A successful reconnect is unchanged.

Fixes: c8efcc786146 ("ksmbd: add support for durable handles v1/v2")
Cc: stable@vger.kernel.org
Signed-off-by: Ian Bridges <icb@fastmail.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/smb2pdu.c   |  9 +++++----
 fs/smb/server/vfs_cache.c | 28 ++++++++++++++++++++++++++++
 fs/smb/server/vfs_cache.h |  2 ++
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 671adf1560c40..ce1432a3ab561 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -5492,6 +5492,8 @@ int smb2_open(struct ksmbd_work *work)
 				ksmbd_close_fd(work, fp->volatile_id);
 				smb2_complete_request_open(work);
 			} else {
+				if (dh_info.reconnected && fp == dh_info.fp)
+					ksmbd_unpublish_reopened_fd(work, fp);
 				ksmbd_fd_put(work, fp);
 			}
 		}
@@ -5505,10 +5507,9 @@ int smb2_open(struct ksmbd_work *work)
 	if (dh_info.reconnected) {
 		/*
 		 * If reconnect succeeded, fp was republished in the
-		 * session file table.  On a later error, ksmbd_fd_put()
-		 * above drops the session reference; drop the durable
-		 * lookup reference through the same session-aware path so
-		 * final close removes the volatile id before freeing fp.
+		 * session file table, and the error path above has
+		 * already removed its volatile id.  Drop the durable
+		 * lookup reference through the same session-aware path.
 		 */
 		if (rc && fp == dh_info.fp)
 			ksmbd_fd_put(work, dh_info.fp);
diff --git a/fs/smb/server/vfs_cache.c b/fs/smb/server/vfs_cache.c
index 119235ec83f7f..1efa9f8145601 100644
--- a/fs/smb/server/vfs_cache.c
+++ b/fs/smb/server/vfs_cache.c
@@ -851,6 +851,34 @@ void ksmbd_wake_session_blocked_works(struct ksmbd_session *sess)
 	read_unlock(&ft->lock);
 }
 
+/**
+ * ksmbd_unpublish_reopened_fd() - remove a reopened durable handle from the
+ *	session file table after its CREATE failed
+ * @work:	smb work of the failed CREATE
+ * @fp:		durable handle republished by ksmbd_reopen_durable_fd()
+ *
+ * The reopen publishes @fp in this session's table without taking a reference
+ * for the entry, so the CREATE error path's puts need not be the last ones.
+ * Another holder of a global-table reference, such as a concurrent reconnect
+ * of the same handle, can drop the last one through ksmbd_put_durable_fd(),
+ * which frees @fp without touching this table.  Remove the id here, while
+ * the caller still holds its references.
+ *
+ * Every path that removes the id before the final put also clears
+ * @fp->volatile_id under ft->lock, so a valid id is still @fp's entry.
+ */
+void ksmbd_unpublish_reopened_fd(struct ksmbd_work *work, struct ksmbd_file *fp)
+{
+	struct ksmbd_file_table *ft = &work->sess->file_table;
+
+	write_lock(&ft->lock);
+	if (has_file_id(fp->volatile_id)) {
+		idr_remove(ft->idr, fp->volatile_id);
+		fp->volatile_id = KSMBD_NO_FID;
+	}
+	write_unlock(&ft->lock);
+}
+
 int ksmbd_close_fd(struct ksmbd_work *work, u64 id)
 {
 	struct ksmbd_file	*fp;
diff --git a/fs/smb/server/vfs_cache.h b/fs/smb/server/vfs_cache.h
index 61238bc4de26e..84ca73f483143 100644
--- a/fs/smb/server/vfs_cache.h
+++ b/fs/smb/server/vfs_cache.h
@@ -198,6 +198,8 @@ static inline bool ksmbd_stream_fd(struct ksmbd_file *fp)
 int ksmbd_init_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);
+void ksmbd_unpublish_reopened_fd(struct ksmbd_work *work,
+				 struct ksmbd_file *fp);
 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);
 struct ksmbd_file *ksmbd_lookup_fd_slow(struct ksmbd_work *work, u64 id,
-- 
2.53.0