Allow times and time system calls to return small negative values

At the moment, the times() system call will appear to fail for a period
shortly after boot, while the value it want to return is between -4095 and
-1.  The same thing will also happen for the time() system call on 32-bit
platforms some time in 2106 or so.

On some platforms, such as x86, this is unavoidable because of the system
call ABI, but other platforms such as powerpc have a separate error
indication from the return value, so system calls can in fact return small
negative values without indicating an error.  On those platforms,
force_successful_syscall_return() provides a way to indicate that the
system call return value should not be treated as an error even if it is
in the range which would normally be taken as a negative error number.

This adds a force_successful_syscall_return() call to the time() and
times() system calls plus their 32-bit compat versions, so that they don't
erroneously indicate an error on those platforms whose system call ABI has
a separate error indication.  This will not affect anything on other
platforms.

Joakim Tjernlund added the fix for time() and the compat versions of
time() and times(), after I did the fix for times().

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: David S. Miller <davem@davemloft.net>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/compat.c

@@ -24,6 +24,7 @@
 #include <linux/migrate.h>
 #include <linux/posix-timers.h>
 #include <linux/times.h>
+#include <linux/ptrace.h>
 
 #include <asm/uaccess.h>
 
@@ -229,6 +230,7 @@ asmlinkage long compat_sys_times(struct compat_tms __user *tbuf)
 		if (copy_to_user(tbuf, &tmp, sizeof(tmp)))
 			return -EFAULT;
 	}
+	force_successful_syscall_return();
 	return compat_jiffies_to_clock_t(jiffies);
 }
 
@@ -894,8 +896,9 @@ asmlinkage long compat_sys_time(compat_time_t __user * tloc)
 
 	if (tloc) {
 		if (put_user(i,tloc))
-			i = -EFAULT;
+			return -EFAULT;
 	}
+	force_successful_syscall_return();
 	return i;
 }
 

kernel/sys.c

@@ -33,6 +33,7 @@
 #include <linux/task_io_accounting_ops.h>
 #include <linux/seccomp.h>
 #include <linux/cpu.h>
+#include <linux/ptrace.h>
 
 #include <linux/compat.h>
 #include <linux/syscalls.h>
@@ -927,6 +928,7 @@ asmlinkage long sys_times(struct tms __user * tbuf)
 		if (copy_to_user(tbuf, &tmp, sizeof(struct tms)))
 			return -EFAULT;
 	}
+	force_successful_syscall_return();
 	return (long) jiffies_64_to_clock_t(get_jiffies_64());
 }
 

kernel/time.c

@@ -37,6 +37,7 @@
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/math64.h>
+#include <linux/ptrace.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -65,8 +66,9 @@ asmlinkage long sys_time(time_t __user * tloc)
 
 	if (tloc) {
 		if (put_user(i,tloc))
-			i = -EFAULT;
+			return -EFAULT;
 	}
+	force_successful_syscall_return();
 	return i;
 }