| Message ID | 1515505362-26760-1-git-send-email-amit.pundir@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [for-3.18.y] perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race | expand |
On Tue, Jan 09, 2018 at 07:12:42PM +0530, Amit Pundir wrote: > From: Peter Zijlstra <peterz@infradead.org> > > commit 321027c1fe77f892f4ea07846aeae08cefbbb290 upstream. > > Di Shen reported a race between two concurrent sys_perf_event_open() > calls where both try and move the same pre-existing software group > into a hardware context. > > The problem is exactly that described in commit: > > f63a8daa5812 ("perf: Fix event->ctx locking") > > ... where, while we wait for a ctx->mutex acquisition, the event->ctx > relation can have changed under us. > > That very same commit failed to recognise sys_perf_event_context() as an > external access vector to the events and thereby didn't apply the > established locking rules correctly. > > So while one sys_perf_event_open() call is stuck waiting on > mutex_lock_double(), the other (which owns said locks) moves the group > about. So by the time the former sys_perf_event_open() acquires the > locks, the context we've acquired is stale (and possibly dead). > > Apply the established locking rules as per perf_event_ctx_lock_nested() > to the mutex_lock_double() for the 'move_group' case. This obviously means > we need to validate state after we acquire the locks. > > Reported-by: Di Shen (Keen Lab) > Tested-by: John Dias <joaodias@google.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Min Chong <mchong@google.com> > 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> > Fixes: f63a8daa5812 ("perf: Fix event->ctx locking") > Link: http://lkml.kernel.org/r/20170106131444.GZ3174@twins.programming.kicks-ass.net > Signed-off-by: Ingo Molnar <mingo@kernel.org> > [bwh: Backported to 3.16: > - Use ACCESS_ONCE() instead of READ_ONCE() > - Test perf_event::group_flags instead of group_caps > - Add the err_locked cleanup block, which we didn't need before > - Adjust context] > Signed-off-by: Ben Hutchings <ben@decadent.org.uk> > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > Signed-off-by: Amit Pundir <amit.pundir@linaro.org> > --- > This upstream patch is featured in recent Android Security bulletin. > Picked up this backported patch from android-3.18. Build tested on 3.18.91 Thanks for this, now queued up. greg k-h
diff --git a/kernel/events/core.c b/kernel/events/core.c index 9b12efcefdf7..de3303aab7d6 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7414,6 +7414,37 @@ static void mutex_lock_double(struct mutex *a, struct mutex *b) mutex_lock_nested(b, SINGLE_DEPTH_NESTING); } +/* + * Variation on perf_event_ctx_lock_nested(), except we take two context + * mutexes. + */ +static struct perf_event_context * +__perf_event_ctx_lock_double(struct perf_event *group_leader, + struct perf_event_context *ctx) +{ + struct perf_event_context *gctx; + +again: + rcu_read_lock(); + gctx = ACCESS_ONCE(group_leader->ctx); + if (!atomic_inc_not_zero(&gctx->refcount)) { + rcu_read_unlock(); + goto again; + } + rcu_read_unlock(); + + mutex_lock_double(&gctx->mutex, &ctx->mutex); + + if (group_leader->ctx != gctx) { + mutex_unlock(&ctx->mutex); + mutex_unlock(&gctx->mutex); + put_ctx(gctx); + goto again; + } + + return gctx; +} + /** * sys_perf_event_open - open a performance event, associate it to a task/cpu * @@ -7626,14 +7657,31 @@ SYSCALL_DEFINE5(perf_event_open, } if (move_group) { - gctx = group_leader->ctx; + gctx = __perf_event_ctx_lock_double(group_leader, ctx); + + /* + * Check if we raced against another sys_perf_event_open() call + * moving the software group underneath us. + */ + if (!(group_leader->group_flags & PERF_GROUP_SOFTWARE)) { + /* + * If someone moved the group out from under us, check + * if this new event wound up on the same ctx, if so + * its the regular !move_group case, otherwise fail. + */ + if (gctx != ctx) { + err = -EINVAL; + goto err_locked; + } else { + perf_event_ctx_unlock(group_leader, gctx); + move_group = 0; + } + } /* * See perf_event_ctx_lock() for comments on the details * of swizzling perf_event::ctx. */ - mutex_lock_double(&gctx->mutex, &ctx->mutex); - perf_remove_from_context(group_leader, false); /* @@ -7674,7 +7722,7 @@ SYSCALL_DEFINE5(perf_event_open, perf_unpin_context(ctx); if (move_group) { - mutex_unlock(&gctx->mutex); + perf_event_ctx_unlock(group_leader, gctx); put_ctx(gctx); } mutex_unlock(&ctx->mutex); @@ -7703,6 +7751,11 @@ SYSCALL_DEFINE5(perf_event_open, fd_install(event_fd, event_file); return event_fd; +err_locked: + if (move_group) + perf_event_ctx_unlock(group_leader, gctx); + mutex_unlock(&ctx->mutex); + fput(event_file); err_context: perf_unpin_context(ctx); put_ctx(ctx);