perf: Fix perf mmap bugs

commit 26cb63ad11e04047a64309362674bcbbd6a6f246 upstream.

Vince reported a problem found by his perf specific trinity
fuzzer.

Al noticed 2 problems with perf's mmap():

 - it has issues against fork() since we use vma->vm_mm for accounting.
 - it has an rb refcount leak on double mmap().

We fix the issues against fork() by using VM_DONTCOPY; I don't
think there's code out there that uses this; we didn't hear
about weird accounting problems/crashes. If we do need this to
work, the previously proposed VM_PINNED could make this work.

Aside from the rb reference leak spotted by Al, Vince's example
prog was indeed doing a double mmap() through the use of
perf_event_set_output().

This exposes another problem, since we now have 2 events with
one buffer, the accounting gets screwy because we account per
event. Fix this by making the buffer responsible for its own
accounting.

[Backporting for 3.4-stable.
VM_RESERVED flag was replaced with pair 'VM_DONTEXPAND | VM_DONTDUMP' in
314e51b9 since 3.7.0-rc1, and 314e51b9 comes from a big patchset, we didn't
backport the patchset, so I restored 'VM_DNOTEXPAND | VM_DONTDUMP' as before:
-       vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP;
+       vma->vm_flags |= VM_DONTCOPY | VM_RESERVED;
 -- zliu]

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Link: http://lkml.kernel.org/r/20130528085548.GA12193@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Zhouping Liu <zliu@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
perf: Fix mmap() accounting hole

commit 9bb5d40cd93c9dd4be74834b1dcb1ba03629716b upstream.

Vince's fuzzer once again found holes. This time it spotted a leak in
the locked page accounting.

When an event had redirected output and its close() was the last
reference to the buffer we didn't have a vm context to undo accounting.

Change the code to destroy the buffer on the last munmap() and detach
all redirected events at that time. This provides us the right context
to undo the vm accounting.

[Backporting for 3.4-stable.
VM_RESERVED flag was replaced with pair 'VM_DONTEXPAND | VM_DONTDUMP' in
314e51b9 since 3.7.0-rc1, and 314e51b9 comes from a big patchset, we didn't
backport the patchset, so I restored 'VM_DNOTEXPAND | VM_DONTDUMP' as before:
-	vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND | VM_DONTDUMP;
+	vma->vm_flags |= VM_DONTCOPY | VM_RESERVED;
 -- zliu]

Reported-and-tested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20130604084421.GI8923@twins.programming.kicks-ass.net
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Zhouping Liu <zliu@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>