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: <83363cbb-2431-4520-81a9-0d71f420cb36@app.fastmail.com>
Date:   Tue, 11 Jul 2023 13:42:19 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Alexey Gladkov" <legion@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "Alexander Viro" <viro@...iv.linux.org.uk>
Cc:     "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 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>