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UPSTREAM: ring-buffer: Prevent overflow of size in ring_buffer_resize()

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(Cherry picked from commit 59643d1535eb220668692a5359de22545af579f6)

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.

Cc: stable@vger.kernel.org # 3.5+
Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic")
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Change-Id: I1147672317a3ad0fc995b1f32baaa050a7976ac4
Bug: 32659848
CVE-2016-9754
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2016-05-13 09:34:12 -04:00 committed by Francescodario Cuzzocrea
parent e212bc1d16
commit 68ad8d0dea
1 changed files with 5 additions and 6 deletions
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11
kernel/trace/ring_buffer.c
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@ -1300,13 +1300,14 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
if (!buffer) if (!buffer)
return size; return size;
size = DIV_ROUND_UP(size, BUF_PAGE_SIZE); nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
size *= BUF_PAGE_SIZE;
buffer_size = buffer->pages * BUF_PAGE_SIZE; buffer_size = buffer->pages * BUF_PAGE_SIZE;
/* we need a minimum of two pages */ /* we need a minimum of two pages */
if (size < BUF_PAGE_SIZE * 2) if (nr_pages < 2)
size = BUF_PAGE_SIZE * 2; nr_pages = 2;
size = nr_pages * BUF_PAGE_SIZE;
if (size == buffer_size) if (size == buffer_size)
return size; return size;
@ -1319,8 +1320,6 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
mutex_lock(&buffer->mutex); mutex_lock(&buffer->mutex);
get_online_cpus(); get_online_cpus();
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
if (size < buffer_size) { if (size < buffer_size) {
/* easy case, just free pages */ /* easy case, just free pages */