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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2016-05-13 09:34:12 -0400
committerSasha Levin <sasha.levin@oracle.com>2016-06-06 19:11:05 -0400
commit180fbec3621c16c23eb5de917577b9aa5dcb1d57 (patch)
tree0bf60c62e6c6d2ad3e3fec0bdb892f5eb3f92a20 /kernel
parenta2d04c9ec64914e94e1a43827fef6089bfeab0b3 (diff)
downloadlinux-linaro-stable-180fbec3621c16c23eb5de917577b9aa5dcb1d57.tar.gz
ring-buffer: Prevent overflow of size in ring_buffer_resize()
[ Upstream 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: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/trace/ring_buffer.c9
1 files changed, 4 insertions, 5 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 9bc154553f8e..d4588b08e07a 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1695,14 +1695,13 @@ 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