linux/arch/mips
Christian Brauner 2a1867219c
fs: add mount_setattr()
This implements the missing mount_setattr() syscall. While the new mount
api allows to change the properties of a superblock there is currently
no way to change the properties of a mount or a mount tree using file
descriptors which the new mount api is based on. In addition the old
mount api has the restriction that mount options cannot be applied
recursively. This hasn't changed since changing mount options on a
per-mount basis was implemented in [1] and has been a frequent request
not just for convenience but also for security reasons. The legacy
mount syscall is unable to accommodate this behavior without introducing
a whole new set of flags because MS_REC | MS_REMOUNT | MS_BIND |
MS_RDONLY | MS_NOEXEC | [...] only apply the mount option to the topmost
mount. Changing MS_REC to apply to the whole mount tree would mean
introducing a significant uapi change and would likely cause significant
regressions.

The new mount_setattr() syscall allows to recursively clear and set
mount options in one shot. Multiple calls to change mount options
requesting the same changes are idempotent:

int mount_setattr(int dfd, const char *path, unsigned flags,
                  struct mount_attr *uattr, size_t usize);

Flags to modify path resolution behavior are specified in the @flags
argument. Currently, AT_EMPTY_PATH, AT_RECURSIVE, AT_SYMLINK_NOFOLLOW,
and AT_NO_AUTOMOUNT are supported. If useful, additional lookup flags to
restrict path resolution as introduced with openat2() might be supported
in the future.

The mount_setattr() syscall can be expected to grow over time and is
designed with extensibility in mind. It follows the extensible syscall
pattern we have used with other syscalls such as openat2(), clone3(),
sched_{set,get}attr(), and others.
The set of mount options is passed in the uapi struct mount_attr which
currently has the following layout:

struct mount_attr {
	__u64 attr_set;
	__u64 attr_clr;
	__u64 propagation;
	__u64 userns_fd;
};

The @attr_set and @attr_clr members are used to clear and set mount
options. This way a user can e.g. request that a set of flags is to be
raised such as turning mounts readonly by raising MOUNT_ATTR_RDONLY in
@attr_set while at the same time requesting that another set of flags is
to be lowered such as removing noexec from a mount tree by specifying
MOUNT_ATTR_NOEXEC in @attr_clr.

Note, since the MOUNT_ATTR_<atime> values are an enum starting from 0,
not a bitmap, users wanting to transition to a different atime setting
cannot simply specify the atime setting in @attr_set, but must also
specify MOUNT_ATTR__ATIME in the @attr_clr field. So we ensure that
MOUNT_ATTR__ATIME can't be partially set in @attr_clr and that @attr_set
can't have any atime bits set if MOUNT_ATTR__ATIME isn't set in
@attr_clr.

The @propagation field lets callers specify the propagation type of a
mount tree. Propagation is a single property that has four different
settings and as such is not really a flag argument but an enum.
Specifically, it would be unclear what setting and clearing propagation
settings in combination would amount to. The legacy mount() syscall thus
forbids the combination of multiple propagation settings too. The goal
is to keep the semantics of mount propagation somewhat simple as they
are overly complex as it is.

The @userns_fd field lets user specify a user namespace whose idmapping
becomes the idmapping of the mount. This is implemented and explained in
detail in the next patch.

[1]: commit 2e4b7fcd92 ("[PATCH] r/o bind mounts: honor mount writer counts at remount")

Link: https://lore.kernel.org/r/20210121131959.646623-35-christian.brauner@ubuntu.com
Cc: David Howells <dhowells@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-api@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
2021-01-24 14:42:45 +01:00
..
alchemy MIPS: Alchemy: Fix memleak in alchemy_clk_setup_cpu 2020-11-17 12:53:57 +01:00
ar7 mips: ar7: add missing iounmap() on error in ar7_gpio_init 2020-11-06 11:32:06 +01:00
ath25 MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
ath79 MIPS: ath79: Remove unused include <asm/mips_machine.h> 2020-07-28 10:20:44 +02:00
bcm47xx MIPS: BCM47XX: fix kconfig dependency bug for BCM47XX_BCMA 2020-11-12 23:21:55 +01:00
bcm63xx MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
bmips dma-direct: rename and cleanup __phys_to_dma 2020-09-11 09:14:43 +02:00
boot MIPS: boot: Fix unaligned access with CONFIG_MIPS_RAW_APPENDED_DTB 2020-12-28 23:26:16 +01:00
cavium-octeon MIPS: OCTEON: fix unreachable code in octeon_irq_init_ciu 2021-01-13 10:59:32 +01:00
cobalt MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
configs MIPS updates for v5.11: 2020-12-16 12:07:54 -08:00
crypto crypto: {arm,arm64,mips}/poly1305 - remove redundant non-reduction from emit 2020-01-16 15:18:12 +08:00
dec MIPS: DEC: Restore bootmem reservation for firmware working memory area 2020-10-14 23:57:57 +02:00
fw MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
generic MIPS: mscc: Add serval support 2020-11-12 23:35:15 +01:00
include local64.h: make <asm/local64.h> mandatory 2020-12-29 15:36:49 -08:00
ingenic MIPS: jz4740: Rename jz4740 folders to ingenic 2020-09-18 16:35:05 +02:00
jazz dma-mapping: merge <linux/dma-noncoherent.h> into <linux/dma-map-ops.h> 2020-10-06 07:07:06 +02:00
kernel fs: add mount_setattr() 2021-01-24 14:42:45 +01:00
kvm MIPS: kvm: Use vm_get_page_prot to get protection bits 2020-11-19 13:26:53 +01:00
lantiq MIPS: lantiq: add missing GPHY clock aliases for ar10 and grx390 2020-08-17 13:01:07 +02:00
lib mips: lib: uncached: fix non-standard usage of variable 'sp' 2020-12-14 16:03:11 +01:00
loongson2ef MIPS updates for v5.10: 2020-10-16 12:40:55 -07:00
loongson32 MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
loongson64 MIPS: Loongson64: Fix up reserving kernel memory range 2020-11-27 10:56:26 +01:00
math-emu MIPS: Use fallthrough for arch/mips 2020-05-07 11:55:47 +02:00
mm MIPS updates for v5.11: 2020-12-16 12:07:54 -08:00
mti-malta MIPS: malta: remove mach-malta/malta-dtshim.h header file 2020-09-21 22:16:47 +02:00
net MIPS: BPF: Use sizeof_field() instead of FIELD_SIZEOF() 2020-01-10 11:33:35 -08:00
netlogic MIPS updates for v5.10: 2020-10-16 12:40:55 -07:00
oprofile mips/oprofile: Fix fallthrough placement 2020-08-22 09:23:15 +02:00
pci mips: Vr41xx: add missing iounmap() on error in vr41xx_pciu_init() 2020-11-06 11:35:46 +01:00
pic32 MIPS: Only include the platform file needed 2020-05-13 00:17:18 +02:00
pistachio MIPS: Fix exception handler memcpy() 2020-05-24 09:15:54 +02:00
power mips: check for dsp presence only once before save/restore 2019-10-07 10:58:53 -07:00
ralink MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
rb532 MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
sgi-ip22 MIPS: Only include the platform file needed 2020-05-13 00:17:18 +02:00
sgi-ip27 mm/sparse: cleanup the code surrounding memory_present() 2020-08-07 11:33:27 -07:00
sgi-ip30 MIPS: SGI-IP30: Move irq bits to better header files 2020-09-21 22:15:49 +02:00
sgi-ip32 MIPS updates for v5.10: 2020-10-16 12:40:55 -07:00
sibyte MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
sni MIPS: SNI: Fix spurious interrupts 2020-09-16 22:40:58 +02:00
tools MIPS: tools: Fix resource leak in elf-entry.c 2020-05-24 09:29:48 +02:00
txx9 MIPS: replace add_memory_region with memblock 2020-10-12 12:01:36 +02:00
vdso mm: forbid splitting special mappings 2020-12-15 12:13:41 -08:00
vr41xx MIPS: Fix builds for VR41xx platforms 2020-05-15 09:09:58 +02:00
Kbuild MIPS: Fix "make clean" error due to recent changes 2020-05-13 13:20:22 +02:00
Kbuild.platforms MIPS: generic: Add support for Ingenic SoCs 2020-09-18 16:33:59 +02:00
Kconfig MIPS updates for v5.11: 2020-12-16 12:07:54 -08:00
Kconfig.debug mips: Add CPS_NS16550_WIDTH config 2020-05-22 09:12:52 +02:00
Makefile mips: boot: add support for self-extracting FIT images (vmlinuz.itb) 2020-11-12 23:47:22 +01:00
Makefile.postlink MIPS: fix indentation of the 'RELOCS' message 2020-01-20 15:37:30 -08:00