Messages in this thread | | | Date | Mon, 01 May 2017 18:35:07 -0500 | From | "Gustavo A. R. Silva" <> | Subject | [usb-host] question about pointer dereference before null check |
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Hello everybody,
While taking a look into Coverity ID 100828 I ran into the following piece of code at drivers/usb/host/ehci-sched.c:1096:
u32 addr; int think_time; int hs_transfers;
addr = dev->ttport << 24; if (!ehci_is_TDI(ehci) || (dev->tt->hub != ehci_to_hcd(ehci)->self.root_hub)) addr |= dev->tt->hub->devnum << 16; addr |= epnum << 8; addr |= dev->devnum; stream->ps.usecs = HS_USECS_ISO(maxp); think_time = dev->tt ? dev->tt->think_time : 0;
The issue here is that dev->tt is being dereferenced before null check.
I was thinking on placing think_time = dev->tt ? dev->tt->think_time : 0; just before the _if_ statement. But this doesn't address the problem of dev->tt actually being NULL.
While looking into the callers of the function containing this piece of code (iso_stream_init()) my impression is that dev->tt is not NULL at the time this function is called and, a very simple patch like the following can be applied in order to avoid the Coverity issue:
-think_time = dev->tt ? dev->tt->think_time : 0; +think_time = dev->tt->think_time;
But I can't tell for sure, so in case dev->tt is NULL, a good strategy to properly update the _addr_ variable would be needed.
What do you think?
I would really appreciate any comment on this, Thank you! -- Gustavo A. R. Silva
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