Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1634051 > unrolled thread
| Started by | "Gustavo A. R. Silva" <garsilva@embeddedor.com> |
|---|---|
| First post | 2017-05-02 02:10 +0200 |
| Last post | 2017-05-02 18:10 +0200 |
| Articles | 3 — 2 participants |
Back to article view | Back to linux.kernel
[usb-host] question about pointer dereference before null check "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-05-02 02:10 +0200
Re: [usb-host] question about pointer dereference before null check Alan Stern <stern@rowland.harvard.edu> - 2017-05-02 16:20 +0200
Re: [usb-host] question about pointer dereference before null check "Gustavo A. R. Silva" <garsilva@embeddedor.com> - 2017-05-02 18:10 +0200
| From | "Gustavo A. R. Silva" <garsilva@embeddedor.com> |
|---|---|
| Date | 2017-05-02 02:10 +0200 |
| Subject | [usb-host] question about pointer dereference before null check |
| Message-ID | <tCty9-7pl-1@gated-at.bofh.it> |
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
[toc] | [next] | [standalone]
| From | Alan Stern <stern@rowland.harvard.edu> |
|---|---|
| Date | 2017-05-02 16:20 +0200 |
| Message-ID | <tCGOK-7Ke-7@gated-at.bofh.it> |
| In reply to | #1634051 |
On Mon, 1 May 2017, Gustavo A. R. Silva wrote: > 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! You are right; udev->tt cannot ever be NULL when this section of code runs. The test should be removed. Alan Stern
[toc] | [prev] | [next] | [standalone]
| From | "Gustavo A. R. Silva" <garsilva@embeddedor.com> |
|---|---|
| Date | 2017-05-02 18:10 +0200 |
| Message-ID | <tCIxc-wA-9@gated-at.bofh.it> |
| In reply to | #1634442 |
Hi Alan, Quoting Alan Stern <stern@rowland.harvard.edu>: > On Mon, 1 May 2017, Gustavo A. R. Silva wrote: > >> 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! > > You are right; udev->tt cannot ever be NULL when this section of code > runs. The test should be removed. > Thanks for confirming, I'll send a patch shortly. -- Gustavo A. R. Silva
[toc] | [prev] | [standalone]
Back to top | Article view | linux.kernel
csiph-web