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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Hongbo Yin <yinhongbo@bytedance.com>,
        Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>,
        Tianci Zhang <zhangtianci.1997@bytedance.com>,
        Miklos Szeredi <mszeredi@redhat.com>
Subject: [PATCH 4.19 020/287] ovl: drop WARN_ON() dentry is NULL in ovl_encode_fh()
Date:   Tue, 23 Aug 2022 10:23:09 +0200
Message-Id: <20220823080100.961392451@linuxfoundation.org>
In-Reply-To: <20220823080100.268827165@linuxfoundation.org>
References: <20220823080100.268827165@linuxfoundation.org>
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From: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>

commit dd524b7f317de8d31d638cbfdc7be4cf9b770e42 upstream.

Some code paths cannot guarantee the inode have any dentry alias. So
WARN_ON() all !dentry may flood the kernel logs.

For example, when an overlayfs inode is watched by inotifywait (1), and
someone is trying to read the /proc/$(pidof inotifywait)/fdinfo/INOTIFY_FD,
at that time if the dentry has been reclaimed by kernel (such as
echo 2 > /proc/sys/vm/drop_caches), there will be a WARN_ON(). The
printed call stack would be like:

    ? show_mark_fhandle+0xf0/0xf0
    show_mark_fhandle+0x4a/0xf0
    ? show_mark_fhandle+0xf0/0xf0
    ? seq_vprintf+0x30/0x50
    ? seq_printf+0x53/0x70
    ? show_mark_fhandle+0xf0/0xf0
    inotify_fdinfo+0x70/0x90
    show_fdinfo.isra.4+0x53/0x70
    seq_show+0x130/0x170
    seq_read+0x153/0x440
    vfs_read+0x94/0x150
    ksys_read+0x5f/0xe0
    do_syscall_64+0x59/0x1e0
    entry_SYSCALL_64_after_hwframe+0x44/0xa9

So let's drop WARN_ON() to avoid kernel log flooding.

Reported-by: Hongbo Yin <yinhongbo@bytedance.com>
Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
Signed-off-by: Tianci Zhang <zhangtianci.1997@bytedance.com>
Fixes: 8ed5eec9d6c4 ("ovl: encode pure upper file handles")
Cc: <stable@vger.kernel.org> # v4.16
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/overlayfs/export.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -277,7 +277,7 @@ static int ovl_encode_fh(struct inode *i
 		return FILEID_INVALID;
 
 	dentry = d_find_any_alias(inode);
-	if (WARN_ON(!dentry))
+	if (!dentry)
 		return FILEID_INVALID;
 
 	type = ovl_dentry_to_fh(dentry, fid, max_len);