Pull misc vfs updates from Christian Brauner:
"Features:
- Reduce pipe->mutex contention by pre-allocating pages outside the
lock in anon_pipe_write().
anon_pipe_write() called alloc_page() once per page while holding
pipe->mutex. The allocation can sleep doing direct reclaim and runs
memcg charging, which extends the critical section and stalls any
concurrent reader on the same mutex. Now up to 8 pages are
pre-allocated before the mutex is taken, leftovers are recycled
into the per-pipe tmp_page[] cache before unlock, and any remainder
is released after unlock, keeping the allocator out of the critical
section on both sides. On a writers x readers sweep with 64KB
writes against a 1 MB pipe throughput improves 6-28% and average
write latency drops 5-22%; under memory pressure - when the cost of
holding the mutex across reclaim is highest - throughput improves
21-48% and latency drops 17-33%. The microbenchmark is added to
selftests.
- uaccess/sockptr: fix the ignored_trailing logic in
copy_struct_to_user() to behave as documented and the usize check
in copy_struct_from_sockptr() for user pointers, and add
copy_struct_{from,to}_bounce_buffer() and copy_struct_to_sockptr()
helpers for upcoming users (IPPROTO_SMBDIRECT, IPPROTO_QUIC).
- bpf: add a sleepable bpf_real_inode() kfunc that resolves the real
inode backing a dentry via d_real_inode(). On overlayfs the inode
attached to the dentry doesn't carry the underlying device
information; this is used by the filesystem restriction BPF program
that was merged into systemd.
- docs: add guidelines for submitting new filesystems, motivated by
the maintenance burden abandoned and untestable filesystems impose
on VFS developers, blocking infrastructure work like folio
conversions and iomap migration.
Fixes:
- libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo()
and drop the now-redundant assignments in callers. This began as a
one-line dma-buf fix for a path_noexec() warning; a pseudo
filesystem has no reason not to set SB_I_NOEXEC. All init_pseudo()
callers were audited: the only visible effect is on dma-buf where
SB_I_NOEXEC silences the warning.
- Handle set_blocksize() failures in legacy filesystems (bfs, hpfs,
qnx4, jfs, befs, affs, isofs, minix, ntfs3, omfs). Mounting a
device with a sector size > PAGE_SIZE crashed roughly half of them;
the rest had the same missing error handling pattern. Plus a
follow-up releasing the superblock buffer_head when setting the
minix v3 block size fails.
- mount: honour SB_NOUSER in the new mount API.
- fs/fcntl: fix a SOFTIRQ-unsafe lock order in fasync signaling by
switching the process-group paths of send_sigio() and send_sigurg()
from read_lock(&tasklist_lock) to RCU, matching the single-PID
path.
- vfs: add an FS_USERNS_DELEGATABLE flag and set it for NFS, fixing
delegated NFS mounts (fsopen() in a container with the mount
performed by a privileged daemon) that broke when non-init
s_user_ns was tied to FS_USERNS_MOUNT.
- selftests/namespaces: fix a hang in nsid_test where an unreaped
grandchild kept the TAP pipe write-end open, a waitpid(-1) race in
listns_efault_test, and a false FAIL on kernels without listns()
where the tests should SKIP.
- filelock: fix the break_lease() stub signature for
CONFIG_FILE_LOCKING=n.
- init/initramfs_test: wait for the async initramfs unpacking before
running; the test and do_populate_rootfs() share the parser state.
- fs/coredump: reduce redundant log noise in
validate_coredump_safety().
- iomap: pass the correct length to fserror_report_io() in
__iomap_write_begin().
- backing-file: fix the backing_file_open() kerneldoc.
Cleanups:
- initramfs: refactor the cpio hex header parsing to use hex2bin()
instead of the hand-rolled simple_strntoul() which is reverted, and
extend the initramfs KUnit tests to cover header fields with 0x
prefixes.
- Replace __get_free_pages() and friends with kmalloc()/kzalloc()
across quota, proc, ocfs2/dlm, nilfs2, nfs, nfsd, libfs, jfs, jbd2,
isofs, fuse, select, namespace, configfs, binfmt_misc, bfs, and the
do_mounts init code - part of the larger work of replacing page
allocator calls with kmalloc().
- Use clear_and_wake_up_bit() in unlock_buffer() and
journal_end_buffer_io_sync() instead of open-coding the sequence.
- Drop unused VFS exports: unexport drop_super_exclusive(), remove
start_removing_user_path_at(), and fold __start_removing_path()
into start_removing_path().
- fs/read_write: narrow the __kernel_write() export with
EXPORT_SYMBOL_FOR_MODULES().
- vfs: uapi: retire octal and hex constants in favor of (1 << n) for
the O_ flags. Finding a free bit for a new flag across the
architectures was needlessly hard with the mixed bases.
- dcache: add extra sanity checks of dead dentries in dentry_free()
via a new DENTRY_WARN_ONCE() that also prints d_flags.
- iov_iter: use kmemdup_array() in dup_iter() to harden the
allocation against multiplication overflow.
- fs/pipe: write to ->poll_usage only once.
- vfs: remove an always-taken if-branch in find_next_fd().
- dcache: use kmalloc_flex() for struct external_name in __d_alloc().
- namei: use QSTR() instead of QSTR_INIT() in path_pts().
- sync_file_range: delete dead S_ISLNK code.
- Comment fixes: retire a stale comment in fget_task_next() and fix
assorted spelling mistakes"
* tag 'vfs-7.2-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (73 commits)
backing-file: fix backing_file_open() kerneldoc parameter
iomap: pass the correct len to fserror_report_io in __iomap_write_begin
vfs: add FS_USERNS_DELEGATABLE flag and set it for NFS
filelock: fix break_lease() stub signature for CONFIG_FILE_LOCKING=n
vfs: uapi: retire octal and hex numbers in favor of (1 << n) for O_ flags
bpf: add bpf_real_inode() kfunc
fs/read_write: Do not export __kernel_write() to the entire world
libfs: drop redundant SB_I_NOEXEC/SB_I_NODEV in init_pseudo() callers
libfs: set SB_I_NOEXEC and SB_I_NODEV by default in init_pseudo()
mount: honour SB_NOUSER in the new mount API
fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling
selftests/pipe: add pipe_bench microbenchmark
fs/pipe: pre-allocate pages outside pipe->mutex in anon_pipe_write
fs: retire stale comment in fget_task_next()
fs: fix spelling mistakes in comment
bfs: replace get_zeroed_page() with kzalloc()
binfmt_misc: replace __get_free_page() with kmalloc()
configfs: replace __get_free_pages() with kzalloc()
fs/namespace: use __getname() to allocate mntpath buffer
fs/select: replace __get_free_page() with kmalloc()
...
poll_get_entry() allocates new memory for poll_table entries using
__get_free_page().
kmalloc() is a better API for such use and it also provides better
scalability and more debugging possibilities.
Replace use of __get_free_page() with kmalloc().
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Link: https://patch.msgid.link/20260523-b4-fs-v1-13-275e36a83f0e@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
kern_select() normalises the user-supplied struct __kernel_old_timeval
with
tv.tv_sec + (tv.tv_usec / USEC_PER_SEC)
(tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC
before calling poll_select_set_timeout() -> timespec64_valid(). Both
operands of the seconds sum are unbounded user-controlled signed long.
A crafted pair where tv_usec is a negative multiple of USEC_PER_SEC
drives the sum across the wrap boundary - e.g.
{ .tv_sec = LONG_MIN, .tv_usec = -1000000 }
yields sec = LONG_MAX, nsec = 0, which passes timespec64_valid() and
then flows through timespec64_add_safe(), which saturates the absolute
deadline to TIME64_MAX (clamped further to KTIME_MAX downstream).
select(2) therefore blocks effectively forever instead of returning
-EINVAL as POSIX requires for a negative timeout.
Only the legacy __NR_select syscall takes this path. pselect6, ppoll,
poll and epoll_pwait2 all hand the user's two fields directly to
poll_select_set_timeout(), which validates *before* doing any
arithmetic:
/* fs/select.c:271 -- the validator */
int poll_select_set_timeout(struct timespec64 *to, time64_t sec, long nsec)
{
struct timespec64 ts = {.tv_sec = sec, .tv_nsec = nsec};
if (!timespec64_valid(&ts))
return -EINVAL;
...
}
/* include/linux/time64.h:97 -- timespec64_valid */
if (ts->tv_sec < 0) return false;
if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC) return false;
/* fs/select.c:744 do_pselect() (pselect6, pselect6_time32) */
if (get_timespec64(&ts, tsp)) return -EFAULT;
if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;
/* fs/select.c:1097 ppoll */
if (get_timespec64(&ts, tsp)) return -EFAULT;
if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;
/* fs/select.c:1065 poll -- timeout_msecs is int; >= 0 gates the math */
if (timeout_msecs >= 0)
poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
/* fs/eventpoll.c:2512 epoll_pwait2 */
if (get_timespec64(&ts, timeout)) return -EFAULT;
if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec)) return -EINVAL;
In every one of these the wrap-prone arithmetic from kern_select()
simply does not exist; the user fields reach timespec64_valid()
unmodified. glibc routes the C-library select() through pselect6,
so the bug is reachable only via a direct syscall(__NR_select, ...).
The pre-validation negative check that used to live here was lost
when the syscall was switched to the poll_select_set_timeout() helper.
Restore it: reject tv_sec < 0 || tv_usec < 0 up front, mirroring what
glibc does in userspace. do_compat_select() has the same arithmetic
pattern but is only reachable on 32-bit compat and from a different
syscall entry; left for a follow-up so this change stays minimal.
Reproducer (returns -1/EINVAL on a fixed kernel; blocks indefinitely
on an unfixed one):
struct timeval tv = { .tv_sec = LONG_MIN, .tv_usec = -1000000 };
fd_set r;
int pfd[2];
pipe(pfd);
FD_ZERO(&r);
FD_SET(pfd[0], &r);
syscall(__NR_select, pfd[0] + 1, &r, NULL, NULL, &tv);
Fixes: 4d36a9e65d ("select: deal with math overflow from borderline valid userland data")
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20260429-timeval-v1-1-4448e2588bbf@debian.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This converts some of the visually simpler cases that have been split
over multiple lines. I only did the ones that are easy to verify the
resulting diff by having just that final GFP_KERNEL argument on the next
line.
Somebody should probably do a proper coccinelle script for this, but for
me the trivial script actually resulted in an assertion failure in the
middle of the script. I probably had made it a bit _too_ trivial.
So after fighting that far a while I decided to just do some of the
syntactically simpler cases with variations of the previous 'sed'
scripts.
The more syntactically complex multi-line cases would mostly really want
whitespace cleanup anyway.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
When running almost any select()/poll() workload intense enough,
KCSAN is likely to report data races around using 'triggered' flag
of 'struct poll_wqueues'. For example, running 'find /' on a tty
console may trigger the following:
BUG: KCSAN: data-race in poll_schedule_timeout / pollwake
write to 0xffffc900030cfb90 of 4 bytes by task 97 on cpu 5:
pollwake+0xd1/0x130
__wake_up_common_lock+0x7f/0xd0
n_tty_receive_buf_common+0x776/0xc30
n_tty_receive_buf2+0x3d/0x60
tty_ldisc_receive_buf+0x6b/0x100
tty_port_default_receive_buf+0x63/0xa0
flush_to_ldisc+0x169/0x3c0
process_scheduled_works+0x6fe/0xf40
worker_thread+0x53b/0x7b0
kthread+0x4f8/0x590
ret_from_fork+0x28c/0x450
ret_from_fork_asm+0x1a/0x30
read to 0xffffc900030cfb90 of 4 bytes by task 5802 on cpu 4:
poll_schedule_timeout+0x96/0x160
do_sys_poll+0x966/0xb30
__se_sys_ppoll+0x1c3/0x210
__x64_sys_ppoll+0x71/0x90
x64_sys_call+0x3079/0x32b0
do_syscall_64+0xfa/0x3b0
entry_SYSCALL_64_after_hwframe+0x77/0x7f
According to Jan, "there's no practical issue here because it is hard
to imagine how the compiler could compile the above code using some
intermediate values stored into 'triggered' or multiple fetches from
'triggered'". Nevertheless, silence KCSAN by using WRITE_ONCE() in
__pollwake() and READ_ONCE() in poll_schedule_timeout(), respectively.
Link: https://lore.kernel.org/linux-fsdevel/bwx72orsztfjx6aoftzzkl7wle3hi4syvusuwc7x36nw6t235e@bjwrosehblty
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Link: https://lore.kernel.org/20250620063059.1800689-1-dmantipov@yandex.ru
Acked-by: Marco Elver <elver@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Adding an unlikely() hint on the n < 0 comparison return path improves
run-time performance of the select() system call, the negative
value of n is very uncommon in normal select usage.
Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with
a 6.15-rc1 kernel built with 14.2.0 using a select of 1000 file
descriptors with zero timeout shows a consistent call reduction from
258 ns down to 254 ns, which is a ~1.5% performance improvement.
Results based on running 25 tests with turbo disabled (to reduce clock
freq turbo changes), with 30 second run per test and comparing the number
of select() calls per second. The % standard deviation of the 25 tests
was 0.24%, so results are reliable.
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/20250414092426.53529-1-colin.i.king@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Adding an unlikely() hint on the fd < 0 comparison return path improves
run-time performance of the poll() system call. gcov based coverage
analysis based on running stress-ng and a kernel build shows that this
path return path is highly unlikely.
Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with
a 6.15-rc1 kernel and a poll of 1024 file descriptors with zero timeout
shows an call reduction from 32818 ns down to 32635 ns, which is a ~0.5%
performance improvement.
Results based on running 25 tests with turbo disabled (to reduce clock
freq turbo changes), with 30 second run per test and comparing the number
of poll() calls per second. The % standard deviation of the 25 tests
was 0.08%, so results are reliable.
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/20250409155510.577490-1-colin.i.king@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
While working on implementing user access validation on powerpc
I got the following warnings on a pmac32_defconfig build:
CC fs/select.o
fs/select.o: warning: objtool: sys_pselect6+0x1bc: redundant UACCESS disable
fs/select.o: warning: objtool: sys_pselect6_time32+0x1bc: redundant UACCESS disable
On powerpc/32s, user_read_access_begin/end() are no-ops, but the
failure path has a user_access_end() instead of user_read_access_end()
which means an access end without any prior access begin.
Replace that user_access_end() by user_read_access_end().
Fixes: 7e71609f64 ("pselect6() and friends: take handling the combined 6th/7th args into helper")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/a7139e28d767a13e667ee3c79599a8047222ef36.1736751221.git.christophe.leroy@csgroup.eu
Signed-off-by: Christian Brauner <brauner@kernel.org>
lift setting ->revents into the caller, so that failure exits (including
the early one) would be plain returns.
We need the scope of our struct fd to end before the store to ->revents,
since that's shared with the failure exits prior to the point where we
can do fdget().
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
take the logics from fdget() to fdput() into an inlined helper - with existing
wait_key_set() subsumed into that.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull 'struct fd' updates from Al Viro:
"Just the 'struct fd' layout change, with conversion to accessor
helpers"
* tag 'pull-stable-struct_fd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
add struct fd constructors, get rid of __to_fd()
struct fd: representation change
introduce fd_file(), convert all accessors to it.
Merge user access fast validation using address masking.
This allows architectures to optionally use a data dependent address
masking model instead of a conditional branch for validating user
accesses. That avoids the Spectre-v1 speculation barriers.
Right now only x86-64 takes advantage of this, and not all architectures
will be able to do it. It requires a guard region between the user and
kernel address spaces (so that you can't overflow from one to the
other), and an easy way to generate a guaranteed-to-fault address for
invalid user pointers.
Also note that this currently assumes that there is no difference
between user read and write accesses. If extended to architectures like
powerpc, we'll also need to separate out the user read-vs-write cases.
* address-masking:
x86: make the masked_user_access_begin() macro use its argument only once
x86: do the user address masking outside the user access area
x86: support user address masking instead of non-speculative conditional
Pull timer updates from Thomas Gleixner:
"Core:
- Overhaul of posix-timers in preparation of removing the workaround
for periodic timers which have signal delivery ignored.
- Remove the historical extra jiffie in msleep()
msleep() adds an extra jiffie to the timeout value to ensure
minimal sleep time. The timer wheel ensures minimal sleep time
since the large rewrite to a non-cascading wheel, but the extra
jiffie in msleep() remained unnoticed. Remove it.
- Make the timer slack handling correct for realtime tasks.
The procfs interface is inconsistent and does neither reflect
reality nor conforms to the man page. Show the correct 0 slack for
real time tasks and enforce it at the core level instead of having
inconsistent individual checks in various timer setup functions.
- The usual set of updates and enhancements all over the place.
Drivers:
- Allow the ACPI PM timer to be turned off during suspend
- No new drivers
- The usual updates and enhancements in various drivers"
* tag 'timers-core-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (43 commits)
ntp: Make sure RTC is synchronized when time goes backwards
treewide: Fix wrong singular form of jiffies in comments
cpu: Use already existing usleep_range()
timers: Rename next_expiry_recalc() to be unique
platform/x86:intel/pmc: Fix comment for the pmc_core_acpi_pm_timer_suspend_resume function
clocksource/drivers/jcore: Use request_percpu_irq()
clocksource/drivers/cadence-ttc: Add missing clk_disable_unprepare in ttc_setup_clockevent
clocksource/drivers/asm9260: Add missing clk_disable_unprepare in asm9260_timer_init
clocksource/drivers/qcom: Add missing iounmap() on errors in msm_dt_timer_init()
clocksource/drivers/ingenic: Use devm_clk_get_enabled() helpers
platform/x86:intel/pmc: Enable the ACPI PM Timer to be turned off when suspended
clocksource: acpi_pm: Add external callback for suspend/resume
clocksource/drivers/arm_arch_timer: Using for_each_available_child_of_node_scoped()
dt-bindings: timer: rockchip: Add rk3576 compatible
timers: Annotate possible non critical data race of next_expiry
timers: Remove historical extra jiffie for timeout in msleep()
hrtimer: Use and report correct timerslack values for realtime tasks
hrtimer: Annotate hrtimer_cpu_base_.*_expiry() for sparse.
timers: Add sparse annotation for timer_sync_wait_running().
signal: Replace BUG_ON()s
...
The timerslack_ns setting is used to specify how much the hardware
timers should be delayed, to potentially dispatch multiple timers in a
single interrupt. This is a performance optimization. Timers of
realtime tasks (having a realtime scheduling policy) should not be
delayed.
This logic was inconsitently applied to the hrtimers, leading to delays
of realtime tasks which used timed waits for events (e.g. condition
variables). Due to the downstream override of the slack for rt tasks,
the procfs reported incorrect (non-zero) timerslack_ns values.
This is changed by setting the timer_slack_ns task attribute to 0 for
all tasks with a rt policy. By that, downstream users do not need to
specially handle rt tasks (w.r.t. the slack), and the procfs entry
shows the correct value of "0". Setting non-zero slack values (either
via procfs or PR_SET_TIMERSLACK) on tasks with a rt policy is ignored,
as stated in "man 2 PR_SET_TIMERSLACK":
Timer slack is not applied to threads that are scheduled under a
real-time scheduling policy (see sched_setscheduler(2)).
The special handling of timerslack on rt tasks in downstream users
is removed as well.
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240814121032.368444-2-felix.moessbauer@siemens.com
The Spectre-v1 mitigations made "access_ok()" much more expensive, since
it has to serialize execution with the test for a valid user address.
All the normal user copy routines avoid this by just masking the user
address with a data-dependent mask instead, but the fast
"unsafe_user_read()" kind of patterms that were supposed to be a fast
case got slowed down.
This introduces a notion of using
src = masked_user_access_begin(src);
to do the user address sanity using a data-dependent mask instead of the
more traditional conditional
if (user_read_access_begin(src, len)) {
model.
This model only works for dense accesses that start at 'src' and on
architectures that have a guard region that is guaranteed to fault in
between the user space and the kernel space area.
With this, the user access doesn't need to be manually checked, because
a bad address is guaranteed to fault (by some architecture masking
trick: on x86-64 this involves just turning an invalid user address into
all ones, since we don't map the top of address space).
This only converts a couple of examples for now. Example x86-64 code
generation for loading two words from user space:
stac
mov %rax,%rcx
sar $0x3f,%rcx
or %rax,%rcx
mov (%rcx),%r13
mov 0x8(%rcx),%r14
clac
where all the error handling and -EFAULT is now purely handled out of
line by the exception path.
Of course, if the micro-architecture does badly at 'clac' and 'stac',
the above is still pitifully slow. But at least we did as well as we
could.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
For any changes of struct fd representation we need to
turn existing accesses to fields into calls of wrappers.
Accesses to struct fd::flags are very few (3 in linux/file.h,
1 in net/socket.c, 3 in fs/overlayfs/file.c and 3 more in
explicit initializers).
Those can be dealt with in the commit converting to
new layout; accesses to struct fd::file are too many for that.
This commit converts (almost) all of f.file to
fd_file(f). It's not entirely mechanical ('file' is used as
a member name more than just in struct fd) and it does not
even attempt to distinguish the uses in pointer context from
those in boolean context; the latter will be eventually turned
into a separate helper (fd_empty()).
NOTE: mass conversion to fd_empty(), tempting as it
might be, is a bad idea; better do that piecewise in commit
that convert from fdget...() to CLASS(...).
[conflicts in fs/fhandle.c, kernel/bpf/syscall.c, mm/memcontrol.c
caught by git; fs/stat.c one got caught by git grep]
[fs/xattr.c conflict]
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
A while ago, we changed the way that select() and poll() preallocate
a temporary buffer just under the size of the static warning limit of
1024 bytes, as clang was frequently going slightly above that limit.
The warnings have recently returned and I took another look. As it turns
out, clang is not actually inherently worse at reserving stack space,
it just happens to inline do_select() into core_sys_select(), while gcc
never inlines it.
Annotate do_select() to never be inlined and in turn remove the special
case for the allocation size. This should give the same behavior for
both clang and gcc all the time and once more avoids those warnings.
Fixes: ad312f95d4 ("fs/select: avoid clang stack usage warning")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20240216202352.2492798-1-arnd@kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
The mix of int, unsigned int, and unsigned long used by struct
poll_list::len, todo, len, and j meant that the signed overflow
sanitizer got worried it needed to instrument several places where
arithmetic happens between these variables. Since all of the variables
are always positive and bounded by unsigned int, use a single type in
all places. Additionally expand the zero-test into an explicit range
check before updating "todo".
This keeps sanitizer instrumentation[1] out of a UACCESS path:
vmlinux.o: warning: objtool: do_sys_poll+0x285: call to __ubsan_handle_sub_overflow() with UACCESS enabled
Link: https://github.com/KSPP/linux/issues/26 [1]
Cc: Christian Brauner <brauner@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>
Cc: <linux-fsdevel@vger.kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20240129184014.work.593-kees@kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
A task can end up indefinitely sleeping in do_select() ->
poll_schedule_timeout() when the following race happens:
TASK1 (thread1) TASK2 TASK1 (thread2)
do_select()
setup poll_wqueues table
with 'fd'
write data to 'fd'
pollwake()
table->triggered = 1
closes 'fd' thread1 is
waiting for
poll_schedule_timeout()
- sees table->triggered
table->triggered = 0
return -EINTR
loop back in do_select()
But at this point when TASK1 loops back, the fdget() in the setup of
poll_wqueues fails. So now so we never find 'fd' is ready for reading
and sleep in poll_schedule_timeout() indefinitely.
Treat an fd that got closed as a fd on which some event happened. This
makes sure cannot block indefinitely in do_select().
Another option would be to return -EBADF in this case but that has a
potential of subtly breaking applications that excercise this behavior
and it happens to work for them. So returning fd as active seems like a
safer choice.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
