From patchwork Wed Dec 11 21:53:03 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Filipe Manana X-Patchwork-Id: 13904282 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 E3EDF1A2872 for ; Wed, 11 Dec 2024 21:53:07 +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=1733953988; cv=none; b=BiQv9vvs729r2t1iUUJtz0iiXyyMyVlJxBGOoDeLbEmuVlbUviejHAZvPx5QZy/rjJzHYnDFrfYFvyGuKHkbeemBy2vOq4q0SL64Tlrrr21+iOrVqqN3S9FWcmBuDLPT9i6S2acyspYn9H4BDfd+VdKTl8Ic3RMY2w9U4KUKixw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733953988; c=relaxed/simple; bh=1YfkVSMgZDAd93B3SAWgYEcerhVtmYjEJRWfQ73V640=; h=From:To:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=HnUqBk2cIpXSzpd3WgiRj+CpeyqKSp7+NxjPaeTlJv3dvHPVn0/F6YwcjIHK5wI9w7GzhRM4EZfaAMekBvdEoJCF9JwF5QXLwD5by7wkFFwrYBLB0QTG4PpwlmrKL0GyniZQh/741c0l4b1DoHMwKs55b6JuAjtjRHsnvq3U8dY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AJotTN7e; 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="AJotTN7e" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DA38AC4CED2 for ; Wed, 11 Dec 2024 21:53:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1733953987; bh=1YfkVSMgZDAd93B3SAWgYEcerhVtmYjEJRWfQ73V640=; h=From:To:Subject:Date:In-Reply-To:References:From; b=AJotTN7ehIvEb/iTAMS7crKzlQZUnRNfvYXp2Je6/5Q4LqP7F6xM3xV/55jxCFKAL GCX12A1tCn/+S4o3Tt9W/g+khNObdX0sevZ84ipeqji4FsLFt5WTqma/ASiT0j4Qbx pJmZqw1/FvxruyV0VCeIbbsAhw/FQPcXGFbpApvSTRzmt35x0ZsaqwMwYUvcjeGqbg 8a0kl/DWlkYU1wZAPz1FybAB9UAFIFUmur87+flRwvwpUqPOnvcS9s97fBWOtciKMR nzFDCcMfDxWUeJUyJ4vVkAbrdOBMnwqPEBZ43bCL7nK0hQo4xelZWJD8jSIrio0a6n Iec8xFelvHOVg== From: fdmanana@kernel.org To: linux-btrfs@vger.kernel.org Subject: [PATCH v2] btrfs: fix use-after-free when COWing tree bock and tracing is enabled Date: Wed, 11 Dec 2024 21:53:03 +0000 Message-Id: <1b96eb7eb9ce220acc21b2ac2057a5a3eab1fb3b.1733953828.git.fdmanana@suse.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <8e502fc69ea68d1647707d947e0e4625f0dd1af0.1733934886.git.fdmanana@suse.com> References: <8e502fc69ea68d1647707d947e0e4625f0dd1af0.1733934886.git.fdmanana@suse.com> Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Filipe Manana When a COWing a tree block, at btrfs_cow_block(), and we have the tracepoint trace_btrfs_cow_block() enabled and preemption is also enabled (CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent buffer while inside the tracepoint code. This is because in some paths that call btrfs_cow_block(), such as btrfs_search_slot(), we are holding the last reference on the extent buffer @buf so btrfs_force_cow_block() drops the last reference on the @buf extent buffer when it calls free_extent_buffer_stale(buf), which schedules the release of the extent buffer with RCU. This means that if we are on a kernel with preemption, the current task may be preempted before calling trace_btrfs_cow_block() and the extent buffer already released by the time trace_btrfs_cow_block() is called, resulting in a use-after-free. Fix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to btrfs_force_cow_block() before the COWed extent buffer is freed. This also has a side effect of invoking the tracepoint in the tree defrag code, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is called there, but this is fine and it was actually missing there. Reported-by: syzbot+8517da8635307182c8a5@syzkaller.appspotmail.com Link: https://lore.kernel.org/linux-btrfs/6759a9b9.050a0220.1ac542.000d.GAE@google.com/ Signed-off-by: Filipe Manana Reviewed-by: Qu Wenruo --- V2: Instead of temporarily bumping the extent buffer's reference count to safely call the tracepoint, move the tracepoint call to btrfs_force_cow_block(). fs/btrfs/ctree.c | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 693dc27ffb89..185985a337b3 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -654,6 +654,8 @@ int btrfs_force_cow_block(struct btrfs_trans_handle *trans, goto error_unlock_cow; } } + + trace_btrfs_cow_block(root, buf, cow); if (unlock_orig) btrfs_tree_unlock(buf); free_extent_buffer_stale(buf); @@ -710,7 +712,6 @@ int btrfs_cow_block(struct btrfs_trans_handle *trans, { struct btrfs_fs_info *fs_info = root->fs_info; u64 search_start; - int ret; if (unlikely(test_bit(BTRFS_ROOT_DELETING, &root->state))) { btrfs_abort_transaction(trans, -EUCLEAN); @@ -751,12 +752,8 @@ int btrfs_cow_block(struct btrfs_trans_handle *trans, * Also We don't care about the error, as it's handled internally. */ btrfs_qgroup_trace_subtree_after_cow(trans, root, buf); - ret = btrfs_force_cow_block(trans, root, buf, parent, parent_slot, - cow_ret, search_start, 0, nest); - - trace_btrfs_cow_block(root, buf, *cow_ret); - - return ret; + return btrfs_force_cow_block(trans, root, buf, parent, parent_slot, + cow_ret, search_start, 0, nest); } ALLOW_ERROR_INJECTION(btrfs_cow_block, ERRNO);