From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AB2F8359F99; Fri, 9 Jan 2026 12:10:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767960643; cv=none; b=i01aRcoj4Pryiy0pwLm41HQFCHoQ/iWYauWyHR+EpsHh6o418L4Dl10q62bI3zOlqiwoL9Xee8/ngtXYxHvGB3xrpjsruLQra45IAyD45QXZODomK3AbqFOn9zfCyZaSZ9J+SSVy/cuzJN+A/my2D9x7vwSYzyWkkLwaQlL6MNs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767960643; c=relaxed/simple; bh=Tnl55jc8tzweAbKVDlQ+JaDbwoFhZgGXiNsda7+diPs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=K3SlULA/xZd/SGw3wQuNJ1vfG5Sj3Wg6O9Q5ilicnHDpeFnH9NtviOTVlyW6MRjGw86sWwGfKyOyk6dBlzJi0wo6uun3he3OSEp5MvBf4CP7Jeo+WQw+nxfQeh2FYWM++zsZmnE6irQHXkvr3yc7BH47FjTgvJDnQspohmezkKs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=deRgRGnv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="deRgRGnv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 374E9C4CEF1; Fri, 9 Jan 2026 12:10:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767960643; bh=Tnl55jc8tzweAbKVDlQ+JaDbwoFhZgGXiNsda7+diPs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=deRgRGnvTL9y9a1mSYde8R/Ib9MqVBG8pa8gCluvyWGK4oC/7y3qsfEVMGFRb7LkZ XX0iySL/pGCrqDDtSV0vIdeABTTp9GI5FpfXah+rD/QRNfdrJQpG3221dwhjbjCyna pNje2wUDkxFkv2vaSC58fEJU3CThluM+cDGpi144= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sudheendra Raghav Neela , Amir Goldstein , Jan Kara Subject: [PATCH 6.6 475/737] fsnotify: do not generate ACCESS/MODIFY events on child for special files Date: Fri, 9 Jan 2026 12:40:14 +0100 Message-ID: <20260109112151.854601020@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260109112133.973195406@linuxfoundation.org> References: <20260109112133.973195406@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Amir Goldstein commit 635bc4def026a24e071436f4f356ea08c0eed6ff upstream. inotify/fanotify do not allow users with no read access to a file to subscribe to events (e.g. IN_ACCESS/IN_MODIFY), but they do allow the same user to subscribe for watching events on children when the user has access to the parent directory (e.g. /dev). Users with no read access to a file but with read access to its parent directory can still stat the file and see if it was accessed/modified via atime/mtime change. The same is not true for special files (e.g. /dev/null). Users will not generally observe atime/mtime changes when other users read/write to special files, only when someone sets atime/mtime via utimensat(). Align fsnotify events with this stat behavior and do not generate ACCESS/MODIFY events to parent watchers on read/write of special files. The events are still generated to parent watchers on utimensat(). This closes some side-channels that could be possibly used for information exfiltration [1]. [1] https://snee.la/pdf/pubs/file-notification-attacks.pdf Reported-by: Sudheendra Raghav Neela CC: stable@vger.kernel.org Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman --- fs/notify/fsnotify.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -224,8 +224,15 @@ int __fsnotify_parent(struct dentry *den /* * Include parent/name in notification either if some notification * groups require parent info or the parent is interested in this event. + * The parent interest in ACCESS/MODIFY events does not apply to special + * files, where read/write are not on the filesystem of the parent and + * events can provide an undesirable side-channel for information + * exfiltration. */ - parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS; + parent_interested = mask & p_mask & ALL_FSNOTIFY_EVENTS && + !(data_type == FSNOTIFY_EVENT_PATH && + d_is_special(dentry) && + (mask & (FS_ACCESS | FS_MODIFY))); if (parent_needed || parent_interested) { /* When notifying parent, child should be passed as data */ WARN_ON_ONCE(inode != fsnotify_data_inode(data, data_type));