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authorGuillaume Knispel <gknispel@proformatique.com>2009-09-22 16:43:30 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 07:39:27 -0700
commit5ae87e79ecb5baa65e9cf48be874098fafad0668 (patch)
tree47dceb61ead03159e93ca998a6f88777474db4f3
parentf58f2fa9286db0ce9124ca9986d56aa5420b7f59 (diff)
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poll/select: avoid arithmetic overflow in __estimate_accuracy()
__estimate_accuracy() was prone to integer overflow, for example if *tv == {2147, 483648000} on a 32 bit computer (or even for delays as small as {429, 500000000} if the task is niced). Because the result was already forced between 0 and 100ms, the effect of the overflow was not too problematic, but the use of the hrtimer range feature was not optimal in overflow cases. This patch ensures that there can not be an integer overflow in this function. Signed-off-by: Guillaume Knispel <gknispel@proformatique.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Arjan van de Ven <arjan@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/select.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/fs/select.c b/fs/select.c
index 8084834e123..a201fc37022 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -41,22 +41,28 @@
* better solutions..
*/
+#define MAX_SLACK (100 * NSEC_PER_MSEC)
+
static long __estimate_accuracy(struct timespec *tv)
{
long slack;
int divfactor = 1000;
+ if (tv->tv_sec < 0)
+ return 0;
+
if (task_nice(current) > 0)
divfactor = divfactor / 5;
+ if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))
+ return MAX_SLACK;
+
slack = tv->tv_nsec / divfactor;
slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);
- if (slack > 100 * NSEC_PER_MSEC)
- slack = 100 * NSEC_PER_MSEC;
+ if (slack > MAX_SLACK)
+ return MAX_SLACK;
- if (slack < 0)
- slack = 0;
return slack;
}