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Subject[78/85] perf: Fix perf mmap bugs
3.2.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Zijlstra <peterz@infradead.org>

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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
include/linux/perf_event.h | 3 +--
kernel/events/core.c | 37 ++++++++++++++++++++-----------------
kernel/events/internal.h | 3 +++
3 files changed, 24 insertions(+), 19 deletions(-)

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -819,8 +819,7 @@ struct perf_event {
/* mmap bits */
struct mutex mmap_mutex;
atomic_t mmap_count;
- int mmap_locked;
- struct user_struct *mmap_user;
+
struct ring_buffer *rb;
struct list_head rb_entry;

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2960,7 +2960,7 @@ static void free_event_rcu(struct rcu_he
kfree(event);
}

-static void ring_buffer_put(struct ring_buffer *rb);
+static bool ring_buffer_put(struct ring_buffer *rb);

static void free_event(struct perf_event *event)
{
@@ -3621,13 +3621,13 @@ static struct ring_buffer *ring_buffer_g
return rb;
}

-static void ring_buffer_put(struct ring_buffer *rb)
+static bool ring_buffer_put(struct ring_buffer *rb)
{
struct perf_event *event, *n;
unsigned long flags;

if (!atomic_dec_and_test(&rb->refcount))
- return;
+ return false;

spin_lock_irqsave(&rb->event_lock, flags);
list_for_each_entry_safe(event, n, &rb->event_list, rb_entry) {
@@ -3637,6 +3637,7 @@ static void ring_buffer_put(struct ring_
spin_unlock_irqrestore(&rb->event_lock, flags);

call_rcu(&rb->rcu_head, rb_free_rcu);
+ return true;
}

static void perf_mmap_open(struct vm_area_struct *vma)
@@ -3651,18 +3652,20 @@ static void perf_mmap_close(struct vm_ar
struct perf_event *event = vma->vm_file->private_data;

if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
- unsigned long size = perf_data_size(event->rb);
- struct user_struct *user = event->mmap_user;
struct ring_buffer *rb = event->rb;
+ struct user_struct *mmap_user = rb->mmap_user;
+ int mmap_locked = rb->mmap_locked;
+ unsigned long size = perf_data_size(rb);

- atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm);
- vma->vm_mm->pinned_vm -= event->mmap_locked;
rcu_assign_pointer(event->rb, NULL);
ring_buffer_detach(event, rb);
mutex_unlock(&event->mmap_mutex);

- ring_buffer_put(rb);
- free_uid(user);
+ if (ring_buffer_put(rb)) {
+ atomic_long_sub((size >> PAGE_SHIFT) + 1, &mmap_user->locked_vm);
+ vma->vm_mm->pinned_vm -= mmap_locked;
+ free_uid(mmap_user);
+ }
}
}

@@ -3715,9 +3718,7 @@ static int perf_mmap(struct file *file,
WARN_ON_ONCE(event->ctx->parent_ctx);
mutex_lock(&event->mmap_mutex);
if (event->rb) {
- if (event->rb->nr_pages == nr_pages)
- atomic_inc(&event->rb->refcount);
- else
+ if (event->rb->nr_pages != nr_pages)
ret = -EINVAL;
goto unlock;
}
@@ -3759,19 +3760,21 @@ static int perf_mmap(struct file *file,
ret = -ENOMEM;
goto unlock;
}
- rcu_assign_pointer(event->rb, rb);
+
+ rb->mmap_locked = extra;
+ rb->mmap_user = get_current_user();

atomic_long_add(user_extra, &user->locked_vm);
- event->mmap_locked = extra;
- event->mmap_user = get_current_user();
- vma->vm_mm->pinned_vm += event->mmap_locked;
+ vma->vm_mm->pinned_vm += extra;
+
+ rcu_assign_pointer(event->rb, rb);

unlock:
if (!ret)
atomic_inc(&event->mmap_count);
mutex_unlock(&event->mmap_mutex);

- vma->vm_flags |= VM_RESERVED;
+ vma->vm_flags |= VM_DONTCOPY | VM_RESERVED;
vma->vm_ops = &perf_mmap_vmops;

return ret;
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -26,6 +26,9 @@ struct ring_buffer {
spinlock_t event_lock;
struct list_head event_list;

+ int mmap_locked;
+ struct user_struct *mmap_user;
+
struct perf_event_mmap_page *user_page;
void *data_pages[0];
};


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