[tip: locking/core] futex: Change utime parameter to be 'const ... *'

[tip-bot2 for Alejandro Colomar]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     3018a08401300005536817507dd14c2a7c4ffa69
Gitweb:        https://git.kernel.org/tip/3018a08401300005536817507dd14c2a7c4ffa69
Author:        Alejandro Colomar <alx.manpages@xxxxxxxxx>
AuthorDate:    Sat, 28 Nov 2020 13:39:46 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 27 Jan 2021 12:30:02 +01:00

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 ]

Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201128123945.4592-1-alx.manpages@xxxxxxxxx
---
 kernel/futex.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index c47d101..d0775aa 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;