On 2016-08-19 06:43 PM, Paul Burton wrote:
Calculating the maximum timeout that a user can set via the
SG_SET_TIMEOUT ioctl involves multiplying INT_MAX by USER_HZ/HZ. If
USER_HZ is larger than HZ then this results in an overflow when
performed as a 32 bit integer calculation, resulting in compiler
warnings such as the following:
drivers/scsi/sg.c: In function 'sg_ioctl':
drivers/scsi/sg.c:91:67: warning: integer overflow in expression [-Woverflow]
#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL))
^
drivers/scsi/sg.c:887:14: note: in expansion of macro 'MULDIV'
if (val >= MULDIV (INT_MAX, USER_HZ, HZ))
^
drivers/scsi/sg.c:91:67: warning: integer overflow in expression [-Woverflow]
#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL))
^
drivers/scsi/sg.c:888:13: note: in expansion of macro 'MULDIV'
val = MULDIV (INT_MAX, USER_HZ, HZ);
^
Avoid this overflow by performing the (constant) arithmetic on 64 bit
integers, which ensures that overflow from multiplying the 32 bit values
cannot occur. When converting the result back to a 32 bit integer use
min_t to ensure that we don't simply truncate a value beyond INT_MAX to
a 32 bit integer, but instead use INT_MAX where the result was larger
than it. As the values are all compile time constant the 64 bit
arithmetic should have no runtime cost.
Signed-off-by: Paul Burton <paul.burton@xxxxxxxxxx>
That macro has been changed several times, hopefully this is the final
time.
Acked by: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
---
drivers/scsi/sg.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index ae7d9bd..bb5ec2d 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -884,8 +884,9 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
return result;
if (val < 0)
return -EIO;
- if (val >= MULDIV (INT_MAX, USER_HZ, HZ))
- val = MULDIV (INT_MAX, USER_HZ, HZ);
+ if (val >= MULDIV((s64)INT_MAX, USER_HZ, HZ))
+ val = min_t(s64, MULDIV((s64)INT_MAX, USER_HZ, HZ),
+ INT_MAX);
sfp->timeout_user = val;
sfp->timeout = MULDIV (val, HZ, USER_HZ);
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
