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Biederman) To: Linus Torvalds Cc: Linux Kernel Mailing List , Oleg Nesterov , Jann Horn , Kees Cook , Greg Ungerer , Rob Landley , Bernd Edlinger , linux-fsdevel , Al Viro , Alexey Dobriyan , Andrew Morton References: <87h7wujhmz.fsf@x220.int.ebiederm.org> <87sgga6ze4.fsf@x220.int.ebiederm.org> <87blmy6zay.fsf_-_@x220.int.ebiederm.org> Date: Sat, 09 May 2020 14:57:33 -0500 In-Reply-To: (Linus Torvalds's message of "Sat, 9 May 2020 12:18:06 -0700") Message-ID: <87k11kyj82.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jXVeh-0002GG-On;;;mid=<87k11kyj82.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX199Tk+7UP647KCMuhUlT5KO3eF9VrjxQc8= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on sa04.xmission.com X-Spam-Level: ** X-Spam-Status: No, score=2.5 required=8.0 tests=ALL_TRUSTED,BAYES_50, DCC_CHECK_NEGATIVE,T_TM2_M_HEADER_IN_MSG,T_TooManySym_01,XMNoVowels, XMSubLong,XM_Body_Dirty_Words autolearn=disabled version=3.4.2 X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.4991] * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.7 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 0; Body=1 Fuz1=1 Fuz2=1] * 0.5 XM_Body_Dirty_Words Contains a dirty word * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: ; sa04 0; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **;Linus Torvalds X-Spam-Relay-Country: X-Spam-Timing: total 441 ms - load_scoreonly_sql: 0.13 (0.0%), signal_user_changed: 13 (3.0%), b_tie_ro: 11 (2.5%), parse: 1.63 (0.4%), extract_message_metadata: 21 (4.7%), get_uri_detail_list: 2.1 (0.5%), tests_pri_-1000: 20 (4.5%), tests_pri_-950: 1.70 (0.4%), tests_pri_-900: 1.49 (0.3%), tests_pri_-90: 82 (18.5%), check_bayes: 80 (18.0%), b_tokenize: 8 (1.9%), b_tok_get_all: 8 (1.8%), b_comp_prob: 2.9 (0.6%), b_tok_touch_all: 56 (12.6%), b_finish: 1.31 (0.3%), tests_pri_0: 281 (63.7%), check_dkim_signature: 0.91 (0.2%), check_dkim_adsp: 12 (2.7%), poll_dns_idle: 0.30 (0.1%), tests_pri_10: 3.9 (0.9%), tests_pri_500: 11 (2.5%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH 3/6] exec: Stop open coding mutex_lock_killable of cred_guard_mutex X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds writes: > On Fri, May 8, 2020 at 11:48 AM Eric W. Biederman wrote: >> >> >> Oleg modified the code that did >> "mutex_lock_interruptible(¤t->cred_guard_mutex)" to return >> -ERESTARTNOINTR instead of -EINTR, so that userspace will never see a >> failure to grab the mutex. >> >> Slightly earlier Liam R. Howlett defined mutex_lock_killable for >> exactly the same situation but it does it a little more cleanly. > > What what what? > > None of this makes sense. Your commit message is completely wrong, and > the patch is utter shite. > > mutex_lock_interruptible() and mutex_lock_killable() are completely > different operations, and the difference has absolutely nothing to do > with -ERESTARTNOINTR or -EINTR. > > mutex_lock_interruptible() is interrupted by any signal. > > mutex_lock_killable() is - surprise surprise - only interrupted by > SIGKILL (in theory any fatal signal, but we never actually implemented > that logic, so it's only interruptible by the known-to-always-be-fatal > SIGKILL). > >> Switch the code to mutex_lock_killable so that it is clearer what the >> code is doing. > > This nonsensical patch makes me worry about all your other patches. > The explanation is wrong, the patch is wrong, and it changes things to > be fundamentally broken. > > Before this, ^C would break out of a blocked execve()/ptrace() > situation. After this patch, you need special tools to do so. > > This patch is completely wrong. Sigh. Brain fart on my part. You are correct. I saw the restart, and totally forgot that it allows the handling of a signal before restarting the system call. Except for the handling of the signal in userspace it is the same as mutex_lock_killable but that is a big big big if. My apologies. I will drop this patch. Eric