futex: Change utime parameter to be 'const ... *'

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 *'.

[ tglx: Make the same change to the compat syscall and fixup the prototypes. ]

Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201128123945.4592-1-alx.manpages@gmail.com

1 files changed, 3 insertions, 3 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index c47d1015d759..d0775aab8da9 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3790,8 +3790,8 @@ 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;
@@ -3986,7 +3986,7 @@ err_unlock:
 
 #ifdef CONFIG_COMPAT_32BIT_TIME
 SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
-		struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
+		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
 		u32, val3)
 {
 	struct timespec64 ts;