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| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2016-05-13 09:34:12 -0400 |
|---|---|---|
| committer | Willy Tarreau <w@1wt.eu> | 2016-06-07 10:42:55 +0200 |
| commit | acd291378f60343d146b0157b64fbca97182c4ea (patch) | |
| tree | 0dcb4a8b1f249a6985cf2635daecfe5090b504ff /kernel | |
| parent | 1b5493498239d8c7087b6c337285b94eb22e98e4 (diff) | |
| download | lwn-acd291378f60343d146b0157b64fbca97182c4ea.tar.gz lwn-acd291378f60343d146b0157b64fbca97182c4ea.zip | |
ring-buffer: Prevent overflow of size in ring_buffer_resize()
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.
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/ring_buffer.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 6f70235770b9..c4ce3a951a1c 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1644,14 +1644,13 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size, !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 |