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* patch "staging: comedi: dt3000: Fix signed integer overflow 'divider * base'" added to staging-linus
@ 2019-08-12 14:48 gregkh
  0 siblings, 0 replies; only message in thread
From: gregkh @ 2019-08-12 14:48 UTC (permalink / raw)
  To: abbotti, dcb314, gregkh, stable

This is a note to let you know that I've just added the patch titled

    staging: comedi: dt3000: Fix signed integer overflow 'divider * base'

to my staging git tree which can be found at
in the staging-linus branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.

If you have any questions about this process, please let me know.

From b4d98bc3fc93ec3a58459948a2c0e0c9b501cd88 Mon Sep 17 00:00:00 2001
From: Ian Abbott <>
Date: Mon, 12 Aug 2019 12:15:17 +0100
Subject: staging: comedi: dt3000: Fix signed integer overflow 'divider * base'

In `dt3k_ns_to_timer()` the following lines near the end of the function
result in a signed integer overflow:

	prescale = 15;
	base = timer_base * (1 << prescale);
	divider = 65535;
	*nanosec = divider * base;

(`divider`, `base` and `prescale` are type `int`, `timer_base` and
`*nanosec` are type `unsigned int`.  The value of `timer_base` will be
either 50 or 100.)

The main reason for the overflow is that the calculation for `base` is
completely wrong.  It should be:

	base = timer_base * (prescale + 1);

which matches an earlier instance of this calculation in the same

Reported-by: David Binderman <>
Cc: <>
Signed-off-by: Ian Abbott <>
Signed-off-by: Greg Kroah-Hartman <>
 drivers/staging/comedi/drivers/dt3000.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/drivers/dt3000.c b/drivers/staging/comedi/drivers/dt3000.c
index 2edf3ee91300..4ad176fc14ad 100644
--- a/drivers/staging/comedi/drivers/dt3000.c
+++ b/drivers/staging/comedi/drivers/dt3000.c
@@ -368,7 +368,7 @@ static int dt3k_ns_to_timer(unsigned int timer_base, unsigned int *nanosec,
 	prescale = 15;
-	base = timer_base * (1 << prescale);
+	base = timer_base * (prescale + 1);
 	divider = 65535;
 	*nanosec = divider * base;
 	return (prescale << 16) | (divider);

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2019-08-12 14:48 patch "staging: comedi: dt3000: Fix signed integer overflow 'divider * base'" added to staging-linus gregkh

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