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

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f3929af..5cb74ed 100644 (file)
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -583,11 +583,11 @@ asmlinkage long sys_unshare(unsigned long unshare_flags);
 
 /* kernel/futex.c */
 asmlinkage long sys_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);
 asmlinkage long sys_futex_time32(u32 __user *uaddr, int op, u32 val,
-                       struct old_timespec32 __user *utime, u32 __user *uaddr2,
-                       u32 val3);
+                                const struct old_timespec32 __user *utime,
+                                u32 __user *uaddr2, u32 val3);
 asmlinkage long sys_get_robust_list(int pid,
                                    struct robust_list_head __user * __user *head_ptr,
                                    size_t __user *len_ptr);

diff --git a/kernel/futex.c b/kernel/futex.c
index c47d101..d0775aa 100644 (file)
--- 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;