From 5ae87e79ecb5baa65e9cf48be874098fafad0668 Mon Sep 17 00:00:00 2001 From: Guillaume Knispel Date: Tue, 22 Sep 2009 16:43:30 -0700 Subject: 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 Cc: Alexander Viro Cc: Arjan van de Ven Cc: Thomas Gleixner Cc: Heiko Carstens Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/select.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/fs/select.c b/fs/select.c index 8084834e123e..a201fc370223 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; } -- cgit