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Date: Fri, 26 Apr 2024 19:38:18 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: cgzones@...glemail.com
Cc: x86@...nel.org, linux-alpha@...r.kernel.org,
 linux-kernel@...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,
 linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
 linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, audit@...r.kernel.org,
 Linux-Arch <linux-arch@...r.kernel.org>, linux-api@...r.kernel.org,
 linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
 "Richard Henderson" <richard.henderson@...aro.org>,
 "Ivan Kokshaysky" <ink@...assic.park.msu.ru>,
 "Matt Turner" <mattst88@...il.com>,
 "Russell King" <linux@...linux.org.uk>,
 "Catalin Marinas" <catalin.marinas@....com>,
 "Will Deacon" <will@...nel.org>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Michal Simek" <monstr@...str.eu>,
 "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "James E . J . Bottomley" <James.Bottomley@...senPartnership.com>,
 "Helge Deller" <deller@....de>, "Michael Ellerman" <mpe@...erman.id.au>,
 "Nicholas Piggin" <npiggin@...il.com>,
 "Christophe Leroy" <christophe.leroy@...roup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 "Heiko Carstens" <hca@...ux.ibm.com>,
 "Vasily Gorbik" <gor@...ux.ibm.com>,
 "Alexander Gordeev" <agordeev@...ux.ibm.com>,
 "Christian Borntraeger" <borntraeger@...ux.ibm.com>,
 "Sven Schnelle" <svens@...ux.ibm.com>,
 "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
 "Rich Felker" <dalias@...c.org>,
 "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>,
 "David S . Miller" <davem@...emloft.net>,
 "Andreas Larsson" <andreas@...sler.com>,
 "Andy Lutomirski" <luto@...nel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>,
 "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, "Chris Zankel" <chris@...kel.net>,
 "Max Filippov" <jcmvbkbc@...il.com>,
 "Alexander Viro" <viro@...iv.linux.org.uk>,
 "Christian Brauner" <brauner@...nel.org>, "Jan Kara" <jack@...e.cz>,
 "Paul Moore" <paul@...l-moore.com>, "Eric Paris" <eparis@...hat.com>,
 "Jens Axboe" <axboe@...nel.dk>,
 "Pavel Begunkov" <asml.silence@...il.com>,
 "Peter Zijlstra" <peterz@...radead.org>,
 "Sohil Mehta" <sohil.mehta@...el.com>,
 "Palmer Dabbelt" <palmer@...ive.com>,
 "Miklos Szeredi" <mszeredi@...hat.com>, "Nhat Pham" <nphamcs@...il.com>,
 "Casey Schaufler" <casey@...aufler-ca.com>,
 "Florian Fainelli" <florian.fainelli@...adcom.com>,
 "Kees Cook" <keescook@...omium.org>,
 "Rick Edgecombe" <rick.p.edgecombe@...el.com>,
 "Mark Rutland" <mark.rutland@....com>, io-uring@...r.kernel.org
Subject: Re: [PATCH v3 2/2] fs/xattr: add *at family syscalls

On Fri, Apr 26, 2024, at 18:20, Christian Göttsche wrote:
> From: Christian Göttsche <cgzones@...glemail.com>
>
> Add the four syscalls setxattrat(), getxattrat(), listxattrat() and
> removexattrat().  Those can be used to operate on extended attributes,
> especially security related ones, either relative to a pinned directory
> or on a file descriptor without read access, avoiding a
> /proc/<pid>/fd/<fd> detour, requiring a mounted procfs.
>
> One use case will be setfiles(8) setting SELinux file contexts
> ("security.selinux") without race conditions and without a file
> descriptor opened with read access requiring SELinux read permission.
>
> Use the do_{name}at() pattern from fs/open.c.
>
> Pass the value of the extended attribute, its length, and for
> setxattrat(2) the command (XATTR_CREATE or XATTR_REPLACE) via an added
> struct xattr_args to not exceed six syscall arguments and not
> merging the AT_* and XATTR_* flags.
>
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> CC: x86@...nel.org
> CC: linux-alpha@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> CC: linux-arm-kernel@...ts.infradead.org
> CC: linux-ia64@...r.kernel.org
> CC: linux-m68k@...ts.linux-m68k.org
> CC: linux-mips@...r.kernel.org
> CC: linux-parisc@...r.kernel.org
> CC: linuxppc-dev@...ts.ozlabs.org
> CC: linux-s390@...r.kernel.org
> CC: linux-sh@...r.kernel.org
> CC: sparclinux@...r.kernel.org
> CC: linux-fsdevel@...r.kernel.org
> CC: audit@...r.kernel.org
> CC: linux-arch@...r.kernel.org
> CC: linux-api@...r.kernel.org
> CC: linux-security-module@...r.kernel.org
> CC: selinux@...r.kernel.org

I checked that the syscalls are all well-formed regarding
argument types, number of arguments and (absence of)
compat handling, and that they are wired up correctly
across architectures

I did not look at the actual implementation in detail.

Reviewed-by: Arnd Bergmann <arnd@...db.de>

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