The patch titled
sys_times() fix return values
has been added to the -mm tree. Its filename is
sys_times-fix-return-values.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: sys_times() fix return values
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
David Brown points out that compat_sys_times() (and sys_times()) can return
arbitrary 32-bit (or 64-bit values). If these happen to be negative (jiffy
wrap, or before INITIAL_JIFFIES) then libc will interpret this as an error and
will return -1 to the libc user and will set errno.
The manpage for times(2) says:
times() returns the number of clock ticks that have elapsed since an
arbitrary point in the past. For Linux 2.4 and earlier this point is
the moment the system was booted. Since Linux 2.6, this point is
(2^32/HZ) - 300 (i.e., about 429 million) seconds before system boot
time. The return value may overflow the possible range of type
clock_t. On error, (clock_t) -1 is returned, and errno is set appro-
priately.
We can fix this by masking the return value down to a 31-bit (63-bit) value.
Also, let's correct for INTIAL_JIFFIES - this isn't a detail which should be
exposed to userspace.
Unfortunately this change can break userspace. If a program was (correctly)
doing:
unsigned long start = times(...);
...
unsigned long end = times(...);
unsigned long delta = end - start;
then `delta' can be grossly wrong if we wrapped in the interval. Instead
userspace will need to mask `delta' by 0x7fffffff (0x7fffffffffffffff) to get
the correct number.
But userspace was already busted in the presence of wraparound, due to glibc's
convert-to-negative-one behaviour.
Given all this stuff, the return value from sys_times() doesn't seem a
particularly useful or reliable kernel interface.
Cc: David Brown <lkml@xxxxxxxxxx>
Cc: Ulrich Drepper <drepper@xxxxxxxxxx>
Cc: Michael Kerrisk <mtk-manpages@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/compat.c | 3 ++-
kernel/sys.c | 3 ++-
2 files changed, 4 insertions(+), 2 deletions(-)
diff -puN kernel/sys.c~sys_times-fix-return-values kernel/sys.c
--- a/kernel/sys.c~sys_times-fix-return-values
+++ a/kernel/sys.c
@@ -897,7 +897,8 @@ asmlinkage long sys_times(struct tms __u
if (copy_to_user(tbuf, &tmp, sizeof(struct tms)))
return -EFAULT;
}
- return (long) jiffies_64_to_clock_t(get_jiffies_64());
+ return jiffies_64_to_clock_t((get_jiffies_64() + INITIAL_JIFFIES) &
+ LONG_MAX);
}
/*
diff -puN kernel/compat.c~sys_times-fix-return-values kernel/compat.c
--- a/kernel/compat.c~sys_times-fix-return-values
+++ a/kernel/compat.c
@@ -162,7 +162,8 @@ asmlinkage long compat_sys_times(struct
if (copy_to_user(tbuf, &tmp, sizeof(tmp)))
return -EFAULT;
}
- return compat_jiffies_to_clock_t(jiffies);
+ return compat_jiffies_to_clock_t((jiffies + INITIAL_JIFFIES) &
+ LONG_MAX);
}
/*
_
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