kernel/linux.git/fs/select.c, branch v7.1-rc5

fs/select: reject negative timeval components in kern_select()

2026-05-12T12:41:40+00:00

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: 4d36a9e65d49 ("select: deal with math overflow from borderline valid userland data") Signed-off-by: Breno Leitao Link: https://patch.msgid.link/20260429-timeval-v1-1-4448e2588bbf@debian.org Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

Merge tag 'vfs-7.1-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-04-13T21:20:11+00:00

Pull misc vfs updates from Christian Brauner: "Features: - coredump: add tracepoint for coredump events - fs: hide file and bfile caches behind runtime const machinery Fixes: - fix architecture-specific compat_ftruncate64 implementations - dcache: Limit the minimal number of bucket to two - fs/omfs: reject s_sys_blocksize smaller than OMFS_DIR_START - fs/mbcache: cancel shrink work before destroying the cache - dcache: permit dynamic_dname()s up to NAME_MAX Cleanups: - remove or unexport unused fs_context infrastructure - trivial ->setattr cleanups - selftests/filesystems: Assume that TIOCGPTPEER is defined - writeback: fix kernel-doc function name mismatch for wb_put_many() - autofs: replace manual symlink buffer allocation in autofs_dir_symlink - init/initramfs.c: trivial fix: FSM -> Finite-state machine - fs: remove stale and duplicate forward declarations - readdir: Introduce dirent_size() - fs: Replace user_access_{begin/end} by scoped user access - kernel: acct: fix duplicate word in comment - fs: write a better comment in step_into() concerning .mnt assignment - fs: attr: fix comment formatting and spelling issues" * tag 'vfs-7.1-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (28 commits) dcache: permit dynamic_dname()s up to NAME_MAX fs: attr: fix comment formatting and spelling issues fs: hide file and bfile caches behind runtime const machinery fs: write a better comment in step_into() concerning .mnt assignment proc: rename proc_notify_change to proc_setattr proc: rename proc_setattr to proc_nochmod_setattr affs: rename affs_notify_change to affs_setattr adfs: rename adfs_notify_change to adfs_setattr hfs: update comments on hfs_inode_setattr kernel: acct: fix duplicate word in comment fs: Replace user_access_{begin/end} by scoped user access readdir: Introduce dirent_size() coredump: add tracepoint for coredump events fs: remove do_sys_truncate fs: pass on FTRUNCATE_* flags to do_truncate fs: fix archiecture-specific compat_ftruncate64 fs: remove stale and duplicate forward declarations init/initramfs.c: trivial fix: FSM -> Finite-state machine autofs: replace manual symlink buffer allocation in autofs_dir_symlink fs/mbcache: cancel shrink work before destroying the cache ...

fs: Replace user_access_{begin/end} by scoped user access

2026-03-24T13:44:02+00:00

Scoped user access reduces code complexity and seamlessly bring masked user access on architectures that support it. Replace user_access_begin/user_access_end blocks by scoped user access. Signed-off-by: Christophe Leroy (CS GROUP) Link: https://patch.msgid.link/16daf33a8190a771a93e294d050bd8153521ffca.1774350128.git.chleroy@kernel.org Signed-off-by: Christian Brauner

Convert more 'alloc_obj' cases to default GFP_KERNEL arguments

2026-02-22T04:03:00+00:00

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

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

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

select: store end_time as timespec64 in restart block

2025-12-24T13:01:57+00:00

Storing the end time seconds as 'unsigned long' can lead to truncation on 32-bit architectures if assigned from the 64-bit timespec64::tv_sec. As the select() core uses timespec64 consistently, also use that in the restart block. This also allows the simplification of the accessors. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251223-restart-block-expiration-v2-1-8e33e5df7359@linutronix.de Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

select: Convert to scoped user access

2025-11-04T07:28:34+00:00

Replace the open coded implementation with the scoped user access guard. No functional change intended. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027083745.862419776@linutronix.de

fs: annotate suspected data race between poll_schedule_timeout() and pollwake()

2025-06-23T10:36:51+00:00

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 Link: https://lore.kernel.org/20250620063059.1800689-1-dmantipov@yandex.ru Acked-by: Marco Elver Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

select: core_sys_select add unlikely branch hint on return path

2025-04-21T08:27:58+00:00

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 Link: https://lore.kernel.org/20250414092426.53529-1-colin.i.king@gmail.com Signed-off-by: Christian Brauner

select: do_pollfd: add unlikely branch hint return path

2025-04-11T13:56:54+00:00

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 Link: https://lore.kernel.org/20250409155510.577490-1-colin.i.king@gmail.com Signed-off-by: Christian Brauner