linux-kernel - [PATCH AUTOSEL 5.14 20/21] cifs: properly invalidate cached root handle when closing it

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Message-Id: <20210917023315.816225-20-sashal@kernel.org>
Date:   Thu, 16 Sep 2021 22:33:14 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Enzo Matsumiya <ematsumiya@...e.de>, Paulo Alcantara <pc@....nz>,
        Steve French <stfrench@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>, sfrench@...ba.org
Subject: [PATCH AUTOSEL 5.14 20/21] cifs: properly invalidate cached root handle when closing it

From: Enzo Matsumiya <ematsumiya@...e.de>

[ Upstream commit 9351590f51cdda49d0265932a37f099950998504 ]

Cached root file was not being completely invalidated sometimes.

Reproducing:
- With a DFS share with 2 targets, one disabled and one enabled
- start some I/O on the mount
  # while true; do ls /mnt/dfs; done
- at the same time, disable the enabled target and enable the disabled
  one
- wait for DFS cache to expire
- on reconnect, the previous cached root handle should be invalid, but
  open_cached_dir_by_dentry() will still try to use it, but throws a
  use-after-free warning (kref_get())

Make smb2_close_cached_fid() invalidate all fields every time, but only
send an SMB2_close() when the entry is still valid.

Signed-off-by: Enzo Matsumiya <ematsumiya@...e.de>
Reviewed-by: Paulo Alcantara (SUSE) <pc@....nz>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/cifs/smb2ops.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 2dfd0d8297eb..1b9de38a136a 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -689,13 +689,19 @@ smb2_close_cached_fid(struct kref *ref)
 		cifs_dbg(FYI, "clear cached root file handle\n");
 		SMB2_close(0, cfid->tcon, cfid->fid->persistent_fid,
 			   cfid->fid->volatile_fid);
-		cfid->is_valid = false;
-		cfid->file_all_info_is_valid = false;
-		cfid->has_lease = false;
-		if (cfid->dentry) {
-			dput(cfid->dentry);
-			cfid->dentry = NULL;
-		}
+	}
+
+	/*
+	 * We only check validity above to send SMB2_close,
+	 * but we still need to invalidate these entries
+	 * when this function is called
+	 */
+	cfid->is_valid = false;
+	cfid->file_all_info_is_valid = false;
+	cfid->has_lease = false;
+	if (cfid->dentry) {
+		dput(cfid->dentry);
+		cfid->dentry = NULL;
 	}
 }
 
-- 
2.30.2