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[209.132.180.67]) by mx.google.com with ESMTP id m1si5764589eji.86.2019.10.06.10.35.01; Sun, 06 Oct 2019 10:35:25 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=SuzX2cwC; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728604AbfJFRb3 (ORCPT + 99 others); Sun, 6 Oct 2019 13:31:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:57706 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729392AbfJFRb1 (ORCPT ); Sun, 6 Oct 2019 13:31:27 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CC2E22133F; Sun, 6 Oct 2019 17:31:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570383086; bh=FbcdFuzSwmId2fZQ0uYOVyPR1pmmmnXDIYZeu+TvAk4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SuzX2cwCI3mW4Z0PiDYL2x47LPRo4hYqGUSGBPsRaogFeVyx9kmvQ1qiULA2zLq0I F3dVi9mzYzgvLoq0vvd30W48gq8DaXJ9tzFuIst8rWraMEYeIsobtecFzdrxr5Rffd S6DTbBM6w10dVmxGGiGmqayJBGL5iEL8BA13Qm9Y= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+bd3bba6ff3fcea7a6ec6@syzkaller.appspotmail.com, Daniel Borkmann , Song Liu , Zubin Mithra , Sasha Levin Subject: [PATCH 4.19 079/106] bpf: fix use after free in prog symbol exposure Date: Sun, 6 Oct 2019 19:21:25 +0200 Message-Id: <20191006171157.020028143@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191006171124.641144086@linuxfoundation.org> References: <20191006171124.641144086@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Borkmann commit c751798aa224fadc5124b49eeb38fb468c0fa039 upstream. syzkaller managed to trigger the warning in bpf_jit_free() which checks via bpf_prog_kallsyms_verify_off() for potentially unlinked JITed BPF progs in kallsyms, and subsequently trips over GPF when walking kallsyms entries: [...] 8021q: adding VLAN 0 to HW filter on device batadv0 8021q: adding VLAN 0 to HW filter on device batadv0 WARNING: CPU: 0 PID: 9869 at kernel/bpf/core.c:810 bpf_jit_free+0x1e8/0x2a0 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 9869 Comm: kworker/0:7 Not tainted 5.0.0-rc8+ #1 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events bpf_prog_free_deferred Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x113/0x167 lib/dump_stack.c:113 panic+0x212/0x40b kernel/panic.c:214 __warn.cold.8+0x1b/0x38 kernel/panic.c:571 report_bug+0x1a4/0x200 lib/bug.c:186 fixup_bug arch/x86/kernel/traps.c:178 [inline] do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973 RIP: 0010:bpf_jit_free+0x1e8/0x2a0 Code: 02 4c 89 e2 83 e2 07 38 d0 7f 08 84 c0 0f 85 86 00 00 00 48 ba 00 02 00 00 00 00 ad de 0f b6 43 02 49 39 d6 0f 84 5f fe ff ff <0f> 0b e9 58 fe ff ff 48 b8 00 00 00 00 00 fc ff df 4c 89 e2 48 c1 RSP: 0018:ffff888092f67cd8 EFLAGS: 00010202 RAX: 0000000000000007 RBX: ffffc90001947000 RCX: ffffffff816e9d88 RDX: dead000000000200 RSI: 0000000000000008 RDI: ffff88808769f7f0 RBP: ffff888092f67d00 R08: fffffbfff1394059 R09: fffffbfff1394058 R10: fffffbfff1394058 R11: ffffffff89ca02c7 R12: ffffc90001947002 R13: ffffc90001947020 R14: ffffffff881eca80 R15: ffff88808769f7e8 BUG: unable to handle kernel paging request at fffffbfff400d000 #PF error: [normal kernel read fault] PGD 21ffee067 P4D 21ffee067 PUD 21ffed067 PMD 9f942067 PTE 0 Oops: 0000 [#1] PREEMPT SMP KASAN CPU: 0 PID: 9869 Comm: kworker/0:7 Not tainted 5.0.0-rc8+ #1 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Workqueue: events bpf_prog_free_deferred RIP: 0010:bpf_get_prog_addr_region kernel/bpf/core.c:495 [inline] RIP: 0010:bpf_tree_comp kernel/bpf/core.c:558 [inline] RIP: 0010:__lt_find include/linux/rbtree_latch.h:115 [inline] RIP: 0010:latch_tree_find include/linux/rbtree_latch.h:208 [inline] RIP: 0010:bpf_prog_kallsyms_find+0x107/0x2e0 kernel/bpf/core.c:632 Code: 00 f0 ff ff 44 38 c8 7f 08 84 c0 0f 85 fa 00 00 00 41 f6 45 02 01 75 02 0f 0b 48 39 da 0f 82 92 00 00 00 48 89 d8 48 c1 e8 03 <42> 0f b6 04 30 84 c0 74 08 3c 03 0f 8e 45 01 00 00 8b 03 48 c1 e0 [...] Upon further debugging, it turns out that whenever we trigger this issue, the kallsyms removal in bpf_prog_ksym_node_del() was /skipped/ but yet bpf_jit_free() reported that the entry is /in use/. Problem is that symbol exposure via bpf_prog_kallsyms_add() but also perf_event_bpf_event() were done /after/ bpf_prog_new_fd(). Once the fd is exposed to the public, a parallel close request came in right before we attempted to do the bpf_prog_kallsyms_add(). Given at this time the prog reference count is one, we start to rip everything underneath us via bpf_prog_release() -> bpf_prog_put(). The memory is eventually released via deferred free, so we're seeing that bpf_jit_free() has a kallsym entry because we added it from bpf_prog_load() but /after/ bpf_prog_put() from the remote CPU. Therefore, move both notifications /before/ we install the fd. The issue was never seen between bpf_prog_alloc_id() and bpf_prog_new_fd() because upon bpf_prog_get_fd_by_id() we'll take another reference to the BPF prog, so we're still holding the original reference from the bpf_prog_load(). Fixes: 6ee52e2a3fe4 ("perf, bpf: Introduce PERF_RECORD_BPF_EVENT") Fixes: 74451e66d516 ("bpf: make jited programs visible in traces") Reported-by: syzbot+bd3bba6ff3fcea7a6ec6@syzkaller.appspotmail.com Signed-off-by: Daniel Borkmann Cc: Song Liu Signed-off-by: Zubin Mithra Signed-off-by: Sasha Levin --- kernel/bpf/syscall.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 118e3a8fc7646..6e544e364821e 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1454,19 +1454,25 @@ static int bpf_prog_load(union bpf_attr *attr) if (err) goto free_used_maps; + /* Upon success of bpf_prog_alloc_id(), the BPF prog is + * effectively publicly exposed. However, retrieving via + * bpf_prog_get_fd_by_id() will take another reference, + * therefore it cannot be gone underneath us. + * + * Only for the time /after/ successful bpf_prog_new_fd() + * and before returning to userspace, we might just hold + * one reference and any parallel close on that fd could + * rip everything out. Hence, below notifications must + * happen before bpf_prog_new_fd(). + * + * Also, any failure handling from this point onwards must + * be using bpf_prog_put() given the program is exposed. + */ + bpf_prog_kallsyms_add(prog); + err = bpf_prog_new_fd(prog); - if (err < 0) { - /* failed to allocate fd. - * bpf_prog_put() is needed because the above - * bpf_prog_alloc_id() has published the prog - * to the userspace and the userspace may - * have refcnt-ed it through BPF_PROG_GET_FD_BY_ID. - */ + if (err < 0) bpf_prog_put(prog); - return err; - } - - bpf_prog_kallsyms_add(prog); return err; free_used_maps: -- 2.20.1