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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,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Haoran Luo <www@aegistudio.net>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>
Subject: [PATCH 4.4 42/47] tracing: Fix bug in rb_per_cpu_empty() that might cause deadloop.
Date: Mon, 26 Jul 2021 17:39:00 +0200	[thread overview]
Message-ID: <20210726153824.301222156@linuxfoundation.org> (raw)
In-Reply-To: <20210726153822.980271128@linuxfoundation.org>

From: Haoran Luo <www@aegistudio.net>

commit 67f0d6d9883c13174669f88adac4f0ee656cc16a upstream.

The "rb_per_cpu_empty()" misinterpret the condition (as not-empty) when
"head_page" and "commit_page" of "struct ring_buffer_per_cpu" points to
the same buffer page, whose "buffer_data_page" is empty and "read" field
is non-zero.

An error scenario could be constructed as followed (kernel perspective):

1. All pages in the buffer has been accessed by reader(s) so that all of
them will have non-zero "read" field.

2. Read and clear all buffer pages so that "rb_num_of_entries()" will
return 0 rendering there's no more data to read. It is also required
that the "read_page", "commit_page" and "tail_page" points to the same
page, while "head_page" is the next page of them.

3. Invoke "ring_buffer_lock_reserve()" with large enough "length"
so that it shot pass the end of current tail buffer page. Now the
"head_page", "commit_page" and "tail_page" points to the same page.

4. Discard current event with "ring_buffer_discard_commit()", so that
"head_page", "commit_page" and "tail_page" points to a page whose buffer
data page is now empty.

When the error scenario has been constructed, "tracing_read_pipe" will
be trapped inside a deadloop: "trace_empty()" returns 0 since
"rb_per_cpu_empty()" returns 0 when it hits the CPU containing such
constructed ring buffer. Then "trace_find_next_entry_inc()" always
return NULL since "rb_num_of_entries()" reports there's no more entry
to read. Finally "trace_seq_to_user()" returns "-EBUSY" spanking
"tracing_read_pipe" back to the start of the "waitagain" loop.

I've also written a proof-of-concept script to construct the scenario
and trigger the bug automatically, you can use it to trace and validate
my reasoning above:

  https://github.com/aegistudio/RingBufferDetonator.git

Tests has been carried out on linux kernel 5.14-rc2
(2734d6c1b1a089fb593ef6a23d4b70903526fe0c), my fixed version
of kernel (for testing whether my update fixes the bug) and
some older kernels (for range of affected kernels). Test result is
also attached to the proof-of-concept repository.

Link: https://lore.kernel.org/linux-trace-devel/YPaNxsIlb2yjSi5Y@aegistudio/
Link: https://lore.kernel.org/linux-trace-devel/YPgrN85WL9VyrZ55@aegistudio

Cc: stable@vger.kernel.org
Fixes: bf41a158cacba ("ring-buffer: make reentrant")
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Signed-off-by: Haoran Luo <www@aegistudio.net>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/ring_buffer.c |   28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3086,10 +3086,30 @@ static bool rb_per_cpu_empty(struct ring
 	if (unlikely(!head))
 		return true;
 
-	return reader->read == rb_page_commit(reader) &&
-		(commit == reader ||
-		 (commit == head &&
-		  head->read == rb_page_commit(commit)));
+	/* Reader should exhaust content in reader page */
+	if (reader->read != rb_page_commit(reader))
+		return false;
+
+	/*
+	 * If writers are committing on the reader page, knowing all
+	 * committed content has been read, the ring buffer is empty.
+	 */
+	if (commit == reader)
+		return true;
+
+	/*
+	 * If writers are committing on a page other than reader page
+	 * and head page, there should always be content to read.
+	 */
+	if (commit != head)
+		return false;
+
+	/*
+	 * Writers are committing on the head page, we just need
+	 * to care about there're committed data, and the reader will
+	 * swap reader page with head page when it is to read data.
+	 */
+	return rb_page_commit(commit) == 0;
 }
 
 /**



  parent reply	other threads:[~2021-07-26 15:42 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 15:38 [PATCH 4.4 00/47] 4.4.277-rc1 review Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 01/47] ARM: brcmstb: dts: fix NAND nodes names Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 02/47] ARM: dts: BCM63xx: Fix " Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 03/47] ARM: dts: imx6: phyFLEX: Fix UART hardware flow control Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 04/47] ARM: imx: pm-imx5: Fix references to imx5_cpu_suspend_info Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 05/47] thermal/core: Correct function name thermal_zone_device_unregister() Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 06/47] kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 07/47] scsi: aic7xxx: Fix unintentional sign extension issue on left shift of u8 Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 08/47] sched/fair: Fix CFS bandwidth hrtimer expiry type Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 09/47] Revert "memory: fsl_ifc: fix leak of IO mapping on probe failure" Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 10/47] x86/fpu: Make init_fpstate correct with optimized XSAVE Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 11/47] net: ipv6: fix return value of ip6_skb_dst_mtu Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 12/47] net: bcmgenet: Ensure all TX/RX queues DMAs are disabled Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 13/47] net: moxa: fix UAF in moxart_mac_probe Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 14/47] net: ti: fix UAF in tlan_remove_one Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 15/47] net: validate lwtstate->data before returning from skb_tunnel_info() Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 16/47] tcp: annotate data races around tp->mtu_info Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 17/47] ipv6: tcp: drop silly ICMPv6 packet too big messages Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 18/47] iavf: Fix an error handling path in iavf_probe() Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 19/47] igb: Check if num of q_vectors is smaller than max before array access Greg Kroah-Hartman
2021-07-26 21:57   ` Pavel Machek
2021-07-26 15:38 ` [PATCH 4.4 20/47] perf test session_topology: Delete session->evlist Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 21/47] perf test bpf: Free obj_buf Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 22/47] perf probe-file: Delete namelist in del_events() on the error path Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 23/47] s390/bpf: Perform r1 range checking before accessing jit->seen_reg[r1] Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 24/47] net: fix uninit-value in caif_seqpkt_sendmsg Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 25/47] net: decnet: Fix sleeping inside in af_decnet Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 26/47] netrom: Decrease sock refcount when sock timers expire Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 27/47] scsi: iscsi: Fix iface sysfs attr detection Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 28/47] scsi: target: Fix protect handling in WRITE SAME(32) Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 29/47] Revert "USB: quirks: ignore remote wake-up on Fibocom L850-GL LTE modem" Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 30/47] proc: Avoid mixing integer types in mem_rw() Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 31/47] s390/ftrace: fix ftrace_update_ftrace_func implementation Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 32/47] ALSA: sb: Fix potential ABBA deadlock in CSP driver Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 33/47] xhci: Fix lost USB 2 remote wake Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 34/47] KVM: PPC: Book3S: Fix H_RTAS rets buffer overflow Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 35/47] usb: hub: Disable USB 3 device initiated lpm if exit latency is too high Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 36/47] USB: usb-storage: Add LaCie Rugged USB3-FW to IGNORE_UAS Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 37/47] usb: max-3421: Prevent corruption of freed memory Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 38/47] usb: renesas_usbhs: Fix superfluous irqs happen after usb_pkt_pop() Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 39/47] USB: serial: option: add support for u-blox LARA-R6 family Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 40/47] USB: serial: cp210x: fix comments for GE CS1000 Greg Kroah-Hartman
2021-07-26 15:38 ` [PATCH 4.4 41/47] USB: serial: cp210x: add ID for CEL EM3588 USB ZigBee stick Greg Kroah-Hartman
2021-07-26 15:39 ` Greg Kroah-Hartman [this message]
2021-07-26 15:39 ` [PATCH 4.4 43/47] media: ngene: Fix out-of-bounds bug in ngene_command_config_free_buf() Greg Kroah-Hartman
2021-07-26 15:39 ` [PATCH 4.4 44/47] net: bcmgenet: ensure EXT_ENERGY_DET_MASK is clear Greg Kroah-Hartman
2021-07-26 15:39 ` [PATCH 4.4 45/47] iio: accel: bma180: Use explicit member assignment Greg Kroah-Hartman
2021-07-26 15:39 ` [PATCH 4.4 46/47] iio: accel: bma180: Fix BMA25x bandwidth register values Greg Kroah-Hartman
2021-07-26 15:39 ` [PATCH 4.4 47/47] btrfs: compression: dont try to compress if we dont have enough pages Greg Kroah-Hartman
2021-07-27  0:37 ` [PATCH 4.4 00/47] 4.4.277-rc1 review Shuah Khan
2021-07-27  3:49 ` Naresh Kamboju

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