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[PATCH 3.14 06/20] ring-buffer: Prevent overflow of size in ring_buffer_resize()

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3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steven Rostedt (Red Hat) <rostedt@goodmis.org>

commit 59643d1535eb220668692a5359de22545af579f6 upstream.

If the size passed to ring_buffer_resize() is greater than MAX_LONG - BUF_PAGE_SIZE
then the DIV_ROUND_UP() will return zero.

Here's the details:

  # echo 18014398509481980 > /sys/kernel/debug/tracing/buffer_size_kb

tracing_entries_write() processes this and converts kb to bytes.

 18014398509481980 << 10 = 18446744073709547520

and this is passed to ring_buffer_resize() as unsigned long size.

 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);

Where DIV_ROUND_UP(a, b) is (a + b - 1)/b

BUF_PAGE_SIZE is 4080 and here

 18446744073709547520 + 4080 - 1 = 18446744073709551599

where 18446744073709551599 is still smaller than 2^64

 2^64 - 18446744073709551599 = 17

But now 18446744073709551599 / 4080 = 4521260802379792

and size = size * 4080 = 18446744073709551360

This is checked to make sure its still greater than 2 * 4080,
which it is.

Then we convert to the number of buffer pages needed.

 nr_page = DIV_ROUND_UP(size, BUF_PAGE_SIZE)

but this time size is 18446744073709551360 and

 2^64 - (18446744073709551360 + 4080 - 1) = -3823

Thus it overflows and the resulting number is less than 4080, which makes

  3823 / 4080 = 0

an nr_pages is set to this. As we already checked against the minimum that
nr_pages may be, this causes the logic to fail as well, and we crash the
kernel.

There's no reason to have the two DIV_ROUND_UP() (that's just result of
historical code changes), clean up the code and fix this bug.

Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 kernel/trace/ring_buffer.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1645,14 +1645,13 @@ int ring_buffer_resize(struct ring_buffe
 	    !cpumask_test_cpu(cpu_id, buffer->cpumask))
 		return size;
 
-	size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
-	size *= BUF_PAGE_SIZE;
+	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
 
 	/* we need a minimum of two pages */
-	if (size < BUF_PAGE_SIZE * 2)
-		size = BUF_PAGE_SIZE * 2;
+	if (nr_pages < 2)
+		nr_pages = 2;
 
-	nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+	size = nr_pages * BUF_PAGE_SIZE;
 
 	/*
 	 * Don't succeed if resizing is disabled, as a reader might be

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[PATCH 3.14 00/20] 3.14.71-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-30 23:00 +0200
  [PATCH 3.14 09/20] mmc: mmc: Fix partition switch timeout for some eMMCs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:00 +0200
  [PATCH 3.14 13/20] USB: serial: mxuport: fix use-after-free in probe error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 18/20] USB: serial: option: add support for Cinterion PH8 and AHxx Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 08/20] mfd: omap-usb-tll: Fix scheduling while atomic BUG Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 06/20] ring-buffer: Prevent overflow of size in ring_buffer_resize() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 15/20] USB: serial: quatech2: fix use-after-free in probe error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 11/20] mmc: longer timeout for long read time quirk Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 10/20] ACPI / osi: Fix an issue that acpi_osi=!* cannot disable ACPICA internal strings Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 14/20] USB: serial: keyspan: fix use-after-free in probe error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 07/20] crypto: caam - fix caam_jr_alloc() ret code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 17/20] USB: serial: io_edgeport: fix memory leaks in probe error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:10 +0200
  [PATCH 3.14 03/20] remove directory incorrectly tries to set delete on close on non-empty directories Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 04/20] fs/cifs: correctly to anonymous authentication via NTLMSSP Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 20/20] serial: samsung: Reorder the sequence of clock control when call s3c24xx_serial_set_termios() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 02/20] arm/arm64: KVM: Enforce Break-Before-Make on Stage-2 page tables Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 19/20] tty: vt, return error when con_startup fails Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 12/20] Bluetooth: vhci: purge unhandled skbs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 05/20] ring-buffer: Use long for nr_pages to avoid overflow failures Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  [PATCH 3.14 01/20] Btrfs: dont use src fd for printk Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-05-31 00:20 +0200
  Re: [PATCH 3.14 00/20] 3.14.71-stable review Guenter Roeck <linux@roeck-us.net> - 2016-06-01 07:30 +0200
  Re: [PATCH 3.14 00/20] 3.14.71-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-06-01 16:30 +0200
    Re: [PATCH 3.14 00/20] 3.14.71-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-01 18:20 +0200
  Re: [PATCH 3.14 00/20] 3.14.71-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-01 18:20 +0200
    Re: [PATCH 3.14 00/20] 3.14.71-stable review Kevin Hilman <khilman@baylibre.com> - 2016-06-01 19:40 +0200

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