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Subject[v3.0 stable version][PATCH 1/2] ring-buffer: Fix NULL pointer if rb_set_head_page() fails
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The function rb_set_head_page() searches the list of ring buffer
pages for a the page that has the HEAD page flag set. If it does
not find it, it will do a WARN_ON(), disable the ring buffer and
return NULL, as this should never happen.

But if this bug happens to happen, not all callers of this function
can handle a NULL pointer being returned from it. That needs to be
fixed.

Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/ring_buffer.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

Index: linux-test.git/kernel/trace/ring_buffer.c
===================================================================
--- linux-test.git.orig/kernel/trace/ring_buffer.c
+++ linux-test.git/kernel/trace/ring_buffer.c
@@ -2926,6 +2926,8 @@ rb_get_reader_page(struct ring_buffer_pe
* Splice the empty reader page into the list around the head.
*/
reader = rb_set_head_page(cpu_buffer);
+ if (!reader)
+ goto out;
cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
cpu_buffer->reader_page->list.prev = reader->list.prev;





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