From 8184059e93c200757f5c0805dae0f14e880eab5d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 29 Jan 2016 15:17:51 +0100 Subject: [PATCH] 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 Reported-by: Andrey Ryabinin Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Andy Lutomirski Cc: Arnaldo Carvalho de Melo Cc: Arnaldo Carvalho de Melo Cc: Borislav Petkov Cc: Brian Gerst Cc: David Ahern Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Jiri Olsa Cc: Linus Torvalds Cc: Namhyung Kim Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Link: http://lkml.kernel.org/r/20160129141751.GA407@worktop Signed-off-by: Ingo Molnar --- kernel/events/ring_buffer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 1faad2cfdb9e..c61f0cbd308b 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -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; - rb->page_order = ilog2(nr_pages); - rb->nr_pages = !!nr_pages; + if (nr_pages) { + rb->nr_pages = 1; + rb->page_order = ilog2(nr_pages); + } ring_buffer_init(rb, watermark, flags); -- 2.20.1