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Wed, 25 Mar 2026 20:18:15 -0700 (PDT) From: Qing Wang To: peterz@infradead.org Cc: acme@kernel.org, adrian.hunter@intel.com, alexander.shishkin@linux.intel.com, irogers@google.com, james.clark@linaro.org, jolsa@kernel.org, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, mark.rutland@arm.com, mingo@redhat.com, namhyung@kernel.org, syzbot+196a82fd904572696b3c@syzkaller.appspotmail.com, wangqing7171@gmail.com, yuhaocheng035@gmail.com Subject: Re: [PATCH v3] perf/core: Fix refcount bug and potential UAF in perf_mmap Date: Thu, 26 Mar 2026 11:18:06 +0800 Message-Id: <20260326031806.876931-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260325151735.GI3738010@noisy.programming.kicks-ass.net> References: <20260325151735.GI3738010@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, 25 Mar 2026 at 23:17, Peter Zijlstra wrote: > Argh,. why is this hidden in this old thread :/ > > On Wed, Mar 25, 2026 at 06:20:53PM +0800, yuhaocheng035@gmail.com wrote: > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 2c35acc2722b..a3228c587de1 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -6730,9 +6730,10 @@ static void perf_pmu_output_stop(struct perf_event *event); > > * the buffer here, where we still have a VM context. This means we need > > * to detach all events redirecting to us. > > */ > > -static void perf_mmap_close(struct vm_area_struct *vma) > > +static void __perf_mmap_close(struct vm_area_struct *vma, struct perf_event *event, > > + bool holds_event_mmap_lock) > > { > > - struct perf_event *event = vma->vm_file->private_data; > > + struct perf_event *iter_event; > > mapped_f unmapped = get_mapped(event, event_unmapped); > > struct perf_buffer *rb = ring_buffer_get(event); > > struct user_struct *mmap_user = rb->mmap_user; > > @@ -6772,11 +6773,14 @@ static void perf_mmap_close(struct vm_area_struct *vma) > > if (refcount_dec_and_test(&rb->mmap_count)) > > detach_rest = true; > > > > - if (!refcount_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) > > + if ((!holds_event_mmap_lock && > > + !refcount_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) || > > + (holds_event_mmap_lock && !refcount_dec_and_test(&event->mmap_count))) > > goto out_put; > > *groan*, this is horrible. > > Let me have a poke to see if there isn't a saner variant around. I think it's ok to move perf_mmap_close() outside the mutex lock, like this: https://lore.kernel.org/all/20260325153240.GK3739106@noisy.programming.kicks-ass.net/T/#m0f82e8ecdfdfce4acd5121bcb799e864cf05ebf9 diff --git a/kernel/events/core.c b/kernel/events/core.c index 1f5699b339ec..e5ce03ce926d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7485,9 +7485,12 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) */ ret = map_range(event->rb, vma); if (ret) - perf_mmap_close(vma); + goto out_close; } + return 0; +out_close: + perf_mmap_close(vma); return ret; } How do you think? -- Qing