Commit 8184059e authored Jan 29, 2016 by Peter Zijlstra Committed by Ingo Molnar Mar 21, 2016

perf/core: Fix Undefined behaviour in rb_alloc()



Sasha reported:

 [ 3494.030114] UBSAN: Undefined behaviour in kernel/events/ring_buffer.c:685:22
 [ 3494.030647] shift exponent -1 is negative

Andrey spotted that this is because:

  It happens if nr_pages = 0:
     rb->page_order = ilog2(nr_pages);

Fix it by making both assignments conditional on nr_pages; since
otherwise they should both be 0 anyway, and will be because of the
kzalloc() used to allocate the structure.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20160129141751.GA407@worktop


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent e8d8a90f

kernel/events/ring_buffer.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -746,8 +746,10 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)

		rb->user_page = all_buf;
		rb->data_pages[0] = all_buf + PAGE_SIZE;
		if (nr_pages) {
		rb->nr_pages = 1;
		rb->page_order = ilog2(nr_pages);
		rb->nr_pages = !!nr_pages;
		}

		ring_buffer_init(rb, watermark, flags);