[PATCH] scsi: qla2xxx: Fix an integer overflow in sysfs code

[Dan Carpenter]

The value of "size" comes from the user.  When we add "start + size"
it could lead to an integer overflow bug.

It means we vmalloc() a lot more memory than we had intended.  I believe
that on 64 bit systems vmalloc() can succeed even if we ask it to
allocate huge 4GB buffers.  So we would get memory corruption and likely
a crash when we call ha->isp_ops->write_optrom() and ->read_optrom().

Only root can trigger this bug.

Fixes: b7cc176c9eb3 ("[SCSI] qla2xxx: Allow region-based flash-part accesses.")
Reported-by: shqking <shqk...@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>

diff --git a/drivers/scsi/qla2xxx/qla_attr.c b/drivers/scsi/qla2xxx/qla_attr.c
index 75c4b312645e..9ce28c4f9812 100644
--- a/drivers/scsi/qla2xxx/qla_attr.c
+++ b/drivers/scsi/qla2xxx/qla_attr.c
@@ -318,6 +318,8 @@ qla2x00_sysfs_write_optrom_ctl(struct file *filp, struct 
kobject *kobj,
                return -EINVAL;
        if (start > ha->optrom_size)
                return -EINVAL;
+       if (size > ha->optrom_size - start)
+               size = ha->optrom_size - start;
 
        mutex_lock(&ha->optrom_mutex);
        switch (val) {
@@ -343,8 +345,7 @@ qla2x00_sysfs_write_optrom_ctl(struct file *filp, struct 
kobject *kobj,
                }
 
                ha->optrom_region_start = start;
-               ha->optrom_region_size = start + size > ha->optrom_size ?
-                   ha->optrom_size - start : size;
+               ha->optrom_region_size = start + size;
 
                ha->optrom_state = QLA_SREADING;
                ha->optrom_buffer = vmalloc(ha->optrom_region_size);
@@ -417,8 +418,7 @@ qla2x00_sysfs_write_optrom_ctl(struct file *filp, struct 
kobject *kobj,
                }
 
                ha->optrom_region_start = start;
-               ha->optrom_region_size = start + size > ha->optrom_size ?
-                   ha->optrom_size - start : size;
+               ha->optrom_region_size = start + size;
 
                ha->optrom_state = QLA_SWRITING;
                ha->optrom_buffer = vmalloc(ha->optrom_region_size);