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 3902081E for ; Fri, 4 Oct 2024 19:35:43 +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=1728070544; cv=none; b=Po08/Zoe/3T474ky998fWCFYa651MLDAWt4Ay/B855RN1o/g6lwzJId3sFiwu14Si7u+N+XhADmc/+qMEEbmO4ZNots3aRjM356HAthw7wvwwu2PvMY04WsS5Nm2qdtZlYgGrE0XNsL5Hu0Qh/l4FlmBJSRhK6rzwYM9PeA7Dio= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728070544; c=relaxed/simple; bh=FbIVHiY/rbg7WqDXDZGXK07+PNJJ+HGQxWp38nW2jbY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=HXxnJSX/6uBhSMQ/niZ2LJ/ole/LKAKKZGIZ0bNkXgEkUy6/yaK7u1LPqhKied7rqndHE3PUcoUaH4DCM7XMrsghSD7kApk+066cVrZWrJkb8eI3tWE4SfUz1kFTB+99F71KVlp6mMb5bvxRRDB3hjPqQjkgGRm/IB07M0uXbjA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qmdjtxXK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qmdjtxXK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A3FD9C4CEC6; Fri, 4 Oct 2024 19:35:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728070543; bh=FbIVHiY/rbg7WqDXDZGXK07+PNJJ+HGQxWp38nW2jbY=; h=From:To:Cc:Subject:Date:From; b=qmdjtxXKzU3KqRiKfmWuYdRtSEELcgbzOSwoMg0FXkUFegim+lyNOMDzuyPhoeBLT 5QoVD4Akkozb9UUUwueCd7QbQ9qTkcSrGsMXoZqspwEDd2EgdTfS2R/y6v5aZWDp8C 5oqlDQ6UUj6HWXwGY9nwpS2MVsr0IBb1FdVzgKZ2Q8fqhpClWMAdu9WJeQLq5F0k98 rYbVURbRmHK71i/lzH/Yn6SpLqRtFM//J5NkYxFSDyvzjH2+TubvphPgU8jRUgNQ7S f33g87h81S0Fm2aWDDesI7oAAWDF7neK5vrLDnJ/sf7gHfjWHt+iPxzxxnCxTxoKBX QWw5q4eoVl39g== From: Eric Biggers To: stable@vger.kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, Jann Horn , Chao Yu , Jaegeuk Kim Subject: [PATCH 6.1] f2fs: Require FMODE_WRITE for atomic write ioctls Date: Fri, 4 Oct 2024 19:34:41 +0000 Message-ID: <20241004193442.189774-1-ebiggers@kernel.org> X-Mailer: git-send-email 2.47.0.rc0.187.ge670bccf7e-goog Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jann Horn commit 4f5a100f87f32cb65d4bb1ad282a08c92f6f591e upstream. The F2FS ioctls for starting and committing atomic writes check for inode_owner_or_capable(), but this does not give LSMs like SELinux or Landlock an opportunity to deny the write access - if the caller's FSUID matches the inode's UID, inode_owner_or_capable() immediately returns true. There are scenarios where LSMs want to deny a process the ability to write particular files, even files that the FSUID of the process owns; but this can currently partially be bypassed using atomic write ioctls in two ways: - F2FS_IOC_START_ATOMIC_REPLACE + F2FS_IOC_COMMIT_ATOMIC_WRITE can truncate an inode to size 0 - F2FS_IOC_START_ATOMIC_WRITE + F2FS_IOC_ABORT_ATOMIC_WRITE can revert changes another process concurrently made to a file Fix it by requiring FMODE_WRITE for these operations, just like for F2FS_IOC_MOVE_RANGE. Since any legitimate caller should only be using these ioctls when intending to write into the file, that seems unlikely to break anything. Fixes: 88b88a667971 ("f2fs: support atomic writes") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Reviewed-by: Chao Yu Reviewed-by: Eric Biggers Signed-off-by: Jaegeuk Kim Signed-off-by: Eric Biggers --- fs/f2fs/file.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index 62f2521cd955e..2982cc5b37d78 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -2103,10 +2103,13 @@ static int f2fs_ioc_start_atomic_write(struct file *filp) struct f2fs_sb_info *sbi = F2FS_I_SB(inode); struct inode *pinode; loff_t isize; int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(mnt_userns, inode)) return -EACCES; if (!S_ISREG(inode->i_mode)) return -EINVAL; @@ -2200,10 +2203,13 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp) { struct inode *inode = file_inode(filp); struct user_namespace *mnt_userns = file_mnt_user_ns(filp); int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(mnt_userns, inode)) return -EACCES; ret = mnt_want_write_file(filp); if (ret) @@ -2232,10 +2238,13 @@ static int f2fs_ioc_abort_atomic_write(struct file *filp) { struct inode *inode = file_inode(filp); struct user_namespace *mnt_userns = file_mnt_user_ns(filp); int ret; + if (!(filp->f_mode & FMODE_WRITE)) + return -EBADF; + if (!inode_owner_or_capable(mnt_userns, inode)) return -EACCES; ret = mnt_want_write_file(filp); if (ret) base-commit: aa4cd140bba57b7064b4c7a7141bebd336d32087 -- 2.47.0.rc0.187.ge670bccf7e-goog