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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 20sm3429761pfx.116.2020.05.08.22.15.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2020 22:15:43 -0700 (PDT) Date: Fri, 8 May 2020 22:15:43 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Oleg Nesterov , Jann Horn , Greg Ungerer , Rob Landley , Bernd Edlinger , linux-fsdevel@vger.kernel.org, Al Viro , Alexey Dobriyan , Andrew Morton Subject: Re: [PATCH 4/6] exec: Run sync_mm_rss before taking exec_update_mutex Message-ID: <202005082213.8BDD4AC0CC@keescook> References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org> <875zd66za3.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875zd66za3.fsf_-_@x220.int.ebiederm.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 08, 2020 at 01:45:56PM -0500, Eric W. Biederman wrote: > Like exec_mm_release sync_mm_rss is about flushing out the state of > the old_mm, which does not need to happen under exec_update_mutex. > > Make this explicit by moving sync_mm_rss outside of exec_update_mutex. > > Signed-off-by: "Eric W. Biederman" Reviewed-by: Kees Cook Additional thoughts below... > --- > fs/exec.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 11a5c073aa35..15682a1dfee9 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1051,13 +1051,14 @@ static int exec_mmap(struct mm_struct *mm) > tsk = current; > old_mm = current->mm; > exec_mm_release(tsk, old_mm); > + if (old_mm) > + sync_mm_rss(old_mm); > > ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); > if (ret) > return ret; > > if (old_mm) { > - sync_mm_rss(old_mm); > /* > * Make sure that if there is a core dump in progress > * for the old mm, we get out and die instead of going $ git grep exec_mm_release fs/exec.c: exec_mm_release(tsk, old_mm); include/linux/sched/mm.h:extern void exec_mm_release(struct task_struct *, struct mm_struct *); kernel/fork.c:void exec_mm_release(struct task_struct *tsk, struct mm_struct *mm) kernel/fork.c: void exit_mm_release(struct task_struct *tsk, struct mm_struct *mm) { futex_exit_release(tsk); mm_release(tsk, mm); } void exec_mm_release(struct task_struct *tsk, struct mm_struct *mm) { futex_exec_release(tsk); mm_release(tsk, mm); } $ git grep exit_mm_release include/linux/sched/mm.h:extern void exit_mm_release(struct task_struct *, struct mm_struct *); kernel/exit.c: exit_mm_release(current, mm); kernel/fork.c:void exit_mm_release(struct task_struct *tsk, struct mm_struct *mm) kernel/exit.c: exit_mm_release(current, mm); if (!mm) return; sync_mm_rss(mm); It looks to me like both exec_mm_release() and exit_mm_release() could easily have the sync_mm_rss(...) folded into their function bodies and removed from the callers. *shrug* -- Kees Cook