linux-kernel - Re: [PATCH v3 2/5] fs: Add fchmodat4()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZK10BmqxjL/Njbmj@example.org>
Date:   Tue, 11 Jul 2023 17:23:50 +0200
From:   Alexey Gladkov <legion@...nel.org>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Palmer Dabbelt <palmer@...ive.com>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jens Axboe <axboe@...nel.dk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        christian@...uner.io, Rich Felker <dalias@...c.org>,
        "David S . Miller" <davem@...emloft.net>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Helge Deller <deller@....de>,
        David Howells <dhowells@...hat.com>, fenghua.yu@...el.com,
        firoz.khan@...aro.org, Florian Weimer <fweimer@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, glebfm@...linux.org,
        gor@...ux.ibm.com, hare@...e.com, heiko.carstens@...ibm.com,
        "H. Peter Anvin" <hpa@...or.com>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>, jhogan@...nel.org,
        Kim Phillips <kim.phillips@....com>, ldv@...linux.org,
        linux-alpha@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        linuxppc-dev@...ts.ozlabs.org, Andy Lutomirski <luto@...nel.org>,
        Matt Turner <mattst88@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Michal Simek <monstr@...str.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Namhyung Kim <namhyung@...nel.org>, paul.burton@...s.com,
        Paul Mackerras <paulus@...ba.org>,
        Peter Zijlstra <peterz@...radead.org>, ralf@...ux-mips.org,
        rth@...ddle.net, schwidefsky@...ibm.com,
        sparclinux@...r.kernel.org, stefan@...er.ch,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>, tycho@...ho.ws,
        Will Deacon <will@...nel.org>, x86@...nel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [PATCH v3 2/5] fs: Add fchmodat4()

On Tue, Jul 11, 2023 at 04:01:03PM +0200, Christian Brauner wrote:
> On Tue, Jul 11, 2023 at 02:51:01PM +0200, Alexey Gladkov wrote:
> > On Tue, Jul 11, 2023 at 01:52:01PM +0200, Christian Brauner wrote:
> > > On Tue, Jul 11, 2023 at 01:42:19PM +0200, Arnd Bergmann wrote:
> > > > On Tue, Jul 11, 2023, at 13:25, Alexey Gladkov wrote:
> > > > > From: Palmer Dabbelt <palmer@...ive.com>
> > > > >
> > > > > On the userspace side fchmodat(3) is implemented as a wrapper
> > > > > function which implements the POSIX-specified interface. This
> > > > > interface differs from the underlying kernel system call, which does not
> > > > > have a flags argument. Most implementations require procfs [1][2].
> > > > >
> > > > > There doesn't appear to be a good userspace workaround for this issue
> > > > > but the implementation in the kernel is pretty straight-forward.
> > > > >
> > > > > The new fchmodat4() syscall allows to pass the AT_SYMLINK_NOFOLLOW flag,
> > > > > unlike existing fchmodat.
> > > > >
> > > > > [1] 
> > > > > https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/fchmodat.c;h=17eca54051ee28ba1ec3f9aed170a62630959143;hb=a492b1e5ef7ab50c6fdd4e4e9879ea5569ab0a6c#l35
> > > > > [2] 
> > > > > https://git.musl-libc.org/cgit/musl/tree/src/stat/fchmodat.c?id=718f363bc2067b6487900eddc9180c84e7739f80#n28
> > > > >
> > > > > Signed-off-by: Palmer Dabbelt <palmer@...ive.com>
> > > > > Signed-off-by: Alexey Gladkov <legion@...nel.org>
> > > > 
> > > > I don't know the history of why we ended up with the different
> > > > interface, or whether this was done intentionally in the kernel
> > > > or if we want this syscall.
> > > > 
> > > > Assuming this is in fact needed, I double-checked that the
> > > > implementation looks correct to me and is portable to all the
> > > > architectures, without the need for a compat wrapper.
> > > > 
> > > > Acked-by: Arnd Bergmann <arnd@...db.de>
> > > 
> > > The system call itself is useful afaict. But please,
> > > 
> > > s/fchmodat4/fchmodat2/
> > 
> > Sure. I will.
> 
> Thanks. Can you also wire this up for every architecture, please?
> I don't see that this has been done in this series.

Sure. I have already added in all architectures as far as I can tell:

$ diff -s <(find arch/ -name '*.tbl' |sort -u) <(git grep -lw fchmodat2 arch/ |sort -u)
Files /dev/fd/63 and /dev/fd/62 are identical

-- 
Rgrds, legion