Messages in this thread Patch in this message |  | | From | Alejandro Colomar <> | Subject | [PATCH] futex: Change 'utime' parameter to be 'const ... *' | Date | Sat, 28 Nov 2020 13:39:46 +0100 |
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futex(2) says that 'utime' is a pointer to 'const'. The implementation doesn't use 'const'; however, it _never_ modifies the contents of utime.
- futex() either uses 'utime' as a pointer to struct or as a 'u32'.
- In case it's used as a 'u32', it makes a copy of it, and of course it is not dereferenced.
- In case it's used as a 'struct __kernel_timespec __user *', the pointer is not dereferenced inside the futex() definition, and it is only passed to a function: get_timespec64(), which accepts a 'const struct __kernel_timespec __user *'.
context: ........
[[ FUTEX(2) Linux Programmer's Manual FUTEX(2)
NAME futex - fast user-space locking
SYNOPSIS #include <linux/futex.h> #include <stdint.h> #include <sys/time.h>
long futex(uint32_t *uaddr, int futex_op, uint32_t val, const struct timespec *timeout, /* or: uint32_t val2 */ uint32_t *uaddr2, uint32_t val3);
Note: There is no glibc wrapper for this system call; see NOTES. ]]
$ sed -n '/SYSCALL_DEFINE.(futex\>/,/^}/p' linux/kernel/futex.c SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL; u32 val2 = 0; int cmd = op & FUTEX_CMD_MASK;
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || cmd == FUTEX_WAIT_BITSET || cmd == FUTEX_WAIT_REQUEUE_PI)) { if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) return -EFAULT; if (get_timespec64(&ts, utime)) return -EFAULT; if (!timespec64_valid(&ts)) return -EINVAL;
t = timespec64_to_ktime(ts); if (cmd == FUTEX_WAIT) t = ktime_add_safe(ktime_get(), t); else if (!(op & FUTEX_CLOCK_REALTIME)) t = timens_ktime_to_host(CLOCK_MONOTONIC, t); tp = &t; } /* * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. */ if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) val2 = (u32) (unsigned long) utime;
return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); }
$ sed -n '/get_timespec64(/,/;/p' linux/include/linux/time.h int get_timespec64(struct timespec64 *ts, const struct __kernel_timespec __user *uts);
...
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com> ---
Hello Thomas & Ingo,
I'm sorry I couldn't test the change in my computers, as there is a bug since Linux 5.7 where I can't boot (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=974166).
Alex
kernel/futex.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index 00259c7e288e..28577c7d2805 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3792,8 +3792,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, - struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, - u32, val3) + const struct __kernel_timespec __user *, utime, + u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL; -- 2.29.2
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