From: Paul Burton Date: Fri, 19 Aug 2016 16:43:56 +0000 (+0100) Subject: scsi: sg: Avoid overflow when USER_HZ > HZ X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=b9b6e80ad3b11778f1066d698a838bcc86efb6be;p=deliverable%2Flinux.git scsi: sg: Avoid overflow when USER_HZ > HZ 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 Acked-by: Douglas Gilbert Signed-off-by: Martin K. Petersen --- diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index ae7d9bdf409c..bb5ec2d6abdf 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);