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

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Date:   Thu, 28 Jan 2021 12:21:36 -0000
From:   "tip-bot2 for Alejandro Colomar" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Alejandro Colomar <alx.manpages@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: locking/core] futex: Change utime parameter to be 'const ... *'

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

Commit-ID:     1ce53e2c2ac069e7b3c400a427002a70deb4a916
Gitweb:        https://git.kernel.org/tip/1ce53e2c2ac069e7b3c400a427002a70deb4a916
Author:        Alejandro Colomar <alx.manpages@...il.com>
AuthorDate:    Sat, 28 Nov 2020 13:39:46 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 28 Jan 2021 13:20:18 +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 and fixup the prototypes. ]

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

---
 include/linux/syscalls.h | 8 ++++----
 kernel/futex.c           | 6 +++---
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f3929af..5cb74ed 100644
--- 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
--- 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;