| Message ID | 20210522021623.GB1260282@rowland.harvard.edu (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 5cc59c418fde9d02859996707b9d5dfd2941c50b |
| Headers | show |
| Series | [v2] USB: core: WARN if pipe direction != setup packet direction | expand |
On Fri, May 21, 2021 at 10:16:23PM -0400, Alan Stern wrote: > When a control URB is submitted, the direction indicated by URB's pipe > member is supposed to match the direction indicated by the setup > packet's bRequestType member. A mismatch could lead to trouble, > depending on which field the host controller drivers use for > determining the actual direction. > > This shouldn't ever happen; it would represent a careless bug in a > kernel driver somewhere. This patch adds a dev_WARN_ONCE to let > people know about the potential problem. > > Suggested-by: "Geoffrey D. Bennett" <g@b4.vu> > Signed-off-by: Alan Stern <stern@rowland.harvard.edu> > --- > > v2: Use dev_WARN_ONCE instead of dev_WARN Reviewed-by: Johan Hovold <johan@kernel.org> > drivers/usb/core/urb.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: usb-devel/drivers/usb/core/urb.c > =================================================================== > --- usb-devel.orig/drivers/usb/core/urb.c > +++ usb-devel/drivers/usb/core/urb.c > @@ -407,6 +407,9 @@ int usb_submit_urb(struct urb *urb, gfp_ > return -ENOEXEC; > is_out = !(setup->bRequestType & USB_DIR_IN) || > !setup->wLength; > + dev_WARN_ONCE(&dev->dev, (usb_pipeout(urb->pipe) != is_out), > + "BOGUS control dir, pipe %x doesn't match bRequestType %x\n", > + urb->pipe, setup->bRequestType); > } else { > is_out = usb_endpoint_dir_out(&ep->desc); > } Johan
On Fri, May 21, 2021 at 10:16:23PM -0400, Alan Stern wrote: > When a control URB is submitted, the direction indicated by URB's pipe > member is supposed to match the direction indicated by the setup > packet's bRequestType member. A mismatch could lead to trouble, > depending on which field the host controller drivers use for > determining the actual direction. > > This shouldn't ever happen; it would represent a careless bug in a > kernel driver somewhere. This patch adds a dev_WARN_ONCE to let > people know about the potential problem. > > Suggested-by: "Geoffrey D. Bennett" <g@b4.vu> > Signed-off-by: Alan Stern <stern@rowland.harvard.edu> > > --- > > v2: Use dev_WARN_ONCE instead of dev_WARN > > > [as1960b] > > > drivers/usb/core/urb.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: usb-devel/drivers/usb/core/urb.c > =================================================================== > --- usb-devel.orig/drivers/usb/core/urb.c > +++ usb-devel/drivers/usb/core/urb.c > @@ -407,6 +407,9 @@ int usb_submit_urb(struct urb *urb, gfp_ > return -ENOEXEC; > is_out = !(setup->bRequestType & USB_DIR_IN) || > !setup->wLength; > + dev_WARN_ONCE(&dev->dev, (usb_pipeout(urb->pipe) != is_out), > + "BOGUS control dir, pipe %x doesn't match bRequestType %x\n", > + urb->pipe, setup->bRequestType); Note that the above will trigger for requests without a data stage also when the pipe and request type agree in case the direction is IN (due to the !wLength check). According to the spec the direction bit should just be ignored for such requests, but we now mandate that usb_sndpipectrl() is always used (i.e. even when USB_DIR_IN is set). Requiring this seems reasonable, but I did find a couple of media drivers (and syszbot reported another) that did "zero-length" reads. Johan
On Mon, May 24, 2021 at 01:39:44PM +0200, Johan Hovold wrote: > On Fri, May 21, 2021 at 10:16:23PM -0400, Alan Stern wrote: > > When a control URB is submitted, the direction indicated by URB's pipe > > member is supposed to match the direction indicated by the setup > > packet's bRequestType member. A mismatch could lead to trouble, > > depending on which field the host controller drivers use for > > determining the actual direction. > > > > This shouldn't ever happen; it would represent a careless bug in a > > kernel driver somewhere. This patch adds a dev_WARN_ONCE to let > > people know about the potential problem. > > > > Suggested-by: "Geoffrey D. Bennett" <g@b4.vu> > > Signed-off-by: Alan Stern <stern@rowland.harvard.edu> > > > > --- > > > > v2: Use dev_WARN_ONCE instead of dev_WARN > > > > > > [as1960b] > > > > > > drivers/usb/core/urb.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > Index: usb-devel/drivers/usb/core/urb.c > > =================================================================== > > --- usb-devel.orig/drivers/usb/core/urb.c > > +++ usb-devel/drivers/usb/core/urb.c > > @@ -407,6 +407,9 @@ int usb_submit_urb(struct urb *urb, gfp_ > > return -ENOEXEC; > > is_out = !(setup->bRequestType & USB_DIR_IN) || > > !setup->wLength; > > + dev_WARN_ONCE(&dev->dev, (usb_pipeout(urb->pipe) != is_out), > > + "BOGUS control dir, pipe %x doesn't match bRequestType %x\n", > > + urb->pipe, setup->bRequestType); > > Note that the above will trigger for requests without a data stage also > when the pipe and request type agree in case the direction is IN (due to > the !wLength check). Yes. How nitpicky the checking needs to be for control transfers with no data stage is an open question. (And it is unfortunate that the warning message is somewhat misleading for this case.) > According to the spec the direction bit should just be ignored for such > requests, but we now mandate that usb_sndpipectrl() is always used (i.e. > even when USB_DIR_IN is set). There actually is a reason for this. If a host controller driver determines the transfer's direction from the pipe value, we want it to get the correct value. The spec says that transfers with no data stage should be treated like OUT transfers (that is, the handshake stage consists of a zero-length IN transaction), so usb_sndpipectrl() is what should be used always. > Requiring this seems reasonable, but I did find a couple of media > drivers (and syszbot reported another) that did "zero-length" reads. Do you think the check should be weakened for this case (i.e., ignore the direction bit in bRequestType when wLength is 0)? So far it seems that the number of places getting this wrong isn't prohibitively large. Alan Stern PS: Another check we could add is to make sure that the transfer_buffer_length value agrees with wLength. Should I add such a check?
On Mon, May 24, 2021 at 10:47:36AM -0400, Alan Stern wrote: > On Mon, May 24, 2021 at 01:39:44PM +0200, Johan Hovold wrote: > > On Fri, May 21, 2021 at 10:16:23PM -0400, Alan Stern wrote: > > > When a control URB is submitted, the direction indicated by URB's pipe > > > member is supposed to match the direction indicated by the setup > > > packet's bRequestType member. A mismatch could lead to trouble, > > > depending on which field the host controller drivers use for > > > determining the actual direction. > > > > > > This shouldn't ever happen; it would represent a careless bug in a > > > kernel driver somewhere. This patch adds a dev_WARN_ONCE to let > > > people know about the potential problem. > > > > > > Suggested-by: "Geoffrey D. Bennett" <g@b4.vu> > > > Signed-off-by: Alan Stern <stern@rowland.harvard.edu> > > > > > > --- > > > > > > v2: Use dev_WARN_ONCE instead of dev_WARN > > > > > > > > > [as1960b] > > > > > > > > > drivers/usb/core/urb.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > Index: usb-devel/drivers/usb/core/urb.c > > > =================================================================== > > > --- usb-devel.orig/drivers/usb/core/urb.c > > > +++ usb-devel/drivers/usb/core/urb.c > > > @@ -407,6 +407,9 @@ int usb_submit_urb(struct urb *urb, gfp_ > > > return -ENOEXEC; > > > is_out = !(setup->bRequestType & USB_DIR_IN) || > > > !setup->wLength; > > > + dev_WARN_ONCE(&dev->dev, (usb_pipeout(urb->pipe) != is_out), > > > + "BOGUS control dir, pipe %x doesn't match bRequestType %x\n", > > > + urb->pipe, setup->bRequestType); > > > > Note that the above will trigger for requests without a data stage also > > when the pipe and request type agree in case the direction is IN (due to > > the !wLength check). > > Yes. How nitpicky the checking needs to be for control transfers with > no data stage is an open question. (And it is unfortunate that the > warning message is somewhat misleading for this case.) > > > According to the spec the direction bit should just be ignored for such > > requests, but we now mandate that usb_sndpipectrl() is always used (i.e. > > even when USB_DIR_IN is set). > > There actually is a reason for this. If a host controller driver > determines the transfer's direction from the pipe value, we want it to > get the correct value. The spec says that transfers with no data stage > should be treated like OUT transfers (that is, the handshake stage > consists of a zero-length IN transaction), so usb_sndpipectrl() is what > should be used always. Right, and that's partly why I think it seems reasonable to always use usb_sndctrlpipe() for these transfers. But see below. > > Requiring this seems reasonable, but I did find a couple of media > > drivers (and syszbot reported another) that did "zero-length" reads. > > Do you think the check should be weakened for this case (i.e., ignore > the direction bit in bRequestType when wLength is 0)? So far it seems > that the number of places getting this wrong isn't prohibitively large. In a sense the request-type direction bit is already ignored when wLength is zero. The question is if we should ignore the direction bit of the pipe argument, or rather allow it to be IN, when wLength is zero. With the above check now merged, the following transfer triggers the warning: usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), 0, USB_DIR_IN | USB_TYPE_VENDOR, 0x0020, CMD_I2C_DA_RD, NULL, 0, 1000); This request was used by a media driver to determine if a certain i2c register was accessible by attempting to read it without really caring about its value. I changed the above to actually read the value, but this is an example where allowing usb_rcvctrlpipe() might otherwise make sense was it not for the possibility that some HCD could get confused. Changing the above to use usb_sndctrlpipe() while either keeping USB_DIR_IN or dropping USB_DIR_IN (for an I2C read request) does not seem right. The latter could potentially even confuse some firmware even if the direction bit is supposed to be ignored. So far this is the only example I've found where changing to usb_sndctrlpipe() and USB_DIR_OUT isn't obviously correct, but on the other hand just reading the register in question is straight-forward enough and does not require any exceptions in usb_submit_urb(). We could perhaps even go the other way and strengthen the check to warn if USB_DIR_IN is set when wLength is zero... > PS: Another check we could add is to make sure that the > transfer_buffer_length value agrees with wLength. Should I add such a > check? That sounds sensible as some of the HCDs only appears to check transfer_buffer_length when handling the data stage and a mismatch could amount to undefined behaviour (OUT) or perhaps even buffer overruns (IN). Judging from a quick check we don't seem to have any such cases currently so this could be implemented as a submission failure rather than another warning. Johan
On Tue, May 25, 2021 at 02:40:17PM +0200, Johan Hovold wrote: > On Mon, May 24, 2021 at 10:47:36AM -0400, Alan Stern wrote: > > Do you think the check should be weakened for this case (i.e., ignore > > the direction bit in bRequestType when wLength is 0)? So far it seems > > that the number of places getting this wrong isn't prohibitively large. > > In a sense the request-type direction bit is already ignored when > wLength is zero. The question is if we should ignore the direction bit > of the pipe argument, or rather allow it to be IN, when wLength is > zero. > > With the above check now merged, the following transfer triggers the > warning: > > usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), > 0, USB_DIR_IN | USB_TYPE_VENDOR, > 0x0020, CMD_I2C_DA_RD, > NULL, 0, 1000); > > This request was used by a media driver to determine if a certain i2c > register was accessible by attempting to read it without really caring > about its value. > > I changed the above to actually read the value, but this is an example > where allowing usb_rcvctrlpipe() might otherwise make sense was it not > for the possibility that some HCD could get confused. > > Changing the above to use usb_sndctrlpipe() while either keeping > USB_DIR_IN or dropping USB_DIR_IN (for an I2C read request) does not > seem right. The latter could potentially even confuse some firmware even > if the direction bit is supposed to be ignored. > > So far this is the only example I've found where changing to > usb_sndctrlpipe() and USB_DIR_OUT isn't obviously correct, but on the > other hand just reading the register in question is straight-forward > enough and does not require any exceptions in usb_submit_urb(). Okay, yes. This seems like a sufficiently unusual edge case that we don't need to add special code to cater for it. In fact, the direction bit in the pipe for a control transfer is never exposed to the USB device. All the device sees is bRequestType and the data/status packet tokens (IN or OUT), which are dictated by the USB protocol. So the fact that we insist on usb_sndctrlpipe for what will ultimately become an I2C read request is unimportant. > We could perhaps even go the other way and strengthen the check to warn > if USB_DIR_IN is set when wLength is zero... Given that the spec says the direction bit is ignored when wLength is zero, I think we shouldn't do this. > > PS: Another check we could add is to make sure that the > > transfer_buffer_length value agrees with wLength. Should I add such a > > check? > > That sounds sensible as some of the HCDs only appears to check > transfer_buffer_length when handling the data stage and a mismatch could > amount to undefined behaviour (OUT) or perhaps even buffer overruns > (IN). > > Judging from a quick check we don't seem to have any such cases > currently so this could be implemented as a submission failure rather > than another warning. All right; I'll make the submission fail with a -EBADR (invalid request descriptor) error; that seems like a good choice of an obscure and otherwise unused value to match this case. But I'll put in a debugging message, so that anyone who wants to know if this is occurring will have a way to find out. Alan Stern
On Tue, May 25, 2021 at 11:12:08AM -0400, Alan Stern wrote: > On Tue, May 25, 2021 at 02:40:17PM +0200, Johan Hovold wrote: > > On Mon, May 24, 2021 at 10:47:36AM -0400, Alan Stern wrote: > > > Do you think the check should be weakened for this case (i.e., ignore > > > the direction bit in bRequestType when wLength is 0)? So far it seems > > > that the number of places getting this wrong isn't prohibitively large. > > > > In a sense the request-type direction bit is already ignored when > > wLength is zero. The question is if we should ignore the direction bit > > of the pipe argument, or rather allow it to be IN, when wLength is > > zero. > > > > With the above check now merged, the following transfer triggers the > > warning: > > > > usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), > > 0, USB_DIR_IN | USB_TYPE_VENDOR, > > 0x0020, CMD_I2C_DA_RD, > > NULL, 0, 1000); > > > > This request was used by a media driver to determine if a certain i2c > > register was accessible by attempting to read it without really caring > > about its value. > > > > I changed the above to actually read the value, but this is an example > > where allowing usb_rcvctrlpipe() might otherwise make sense was it not > > for the possibility that some HCD could get confused. > > > > Changing the above to use usb_sndctrlpipe() while either keeping > > USB_DIR_IN or dropping USB_DIR_IN (for an I2C read request) does not > > seem right. The latter could potentially even confuse some firmware even > > if the direction bit is supposed to be ignored. > > > > So far this is the only example I've found where changing to > > usb_sndctrlpipe() and USB_DIR_OUT isn't obviously correct, but on the > > other hand just reading the register in question is straight-forward > > enough and does not require any exceptions in usb_submit_urb(). > > Okay, yes. This seems like a sufficiently unusual edge case that we > don't need to add special code to cater for it. > > In fact, the direction bit in the pipe for a control transfer is never > exposed to the USB device. All the device sees is bRequestType and the > data/status packet tokens (IN or OUT), which are dictated by the USB > protocol. So the fact that we insist on usb_sndctrlpipe for what will > ultimately become an I2C read request is unimportant. Right, it just looks a bit weird to use usb_sndctrlpipe() with USB_DIR_IN, but that should be fine especially as such cases appears to be rare. > > We could perhaps even go the other way and strengthen the check to warn > > if USB_DIR_IN is set when wLength is zero... > > Given that the spec says the direction bit is ignored when wLength is > zero, I think we shouldn't do this. I agree, let's just allow this. > > > PS: Another check we could add is to make sure that the > > > transfer_buffer_length value agrees with wLength. Should I add such a > > > check? > > > > That sounds sensible as some of the HCDs only appears to check > > transfer_buffer_length when handling the data stage and a mismatch could > > amount to undefined behaviour (OUT) or perhaps even buffer overruns > > (IN). > > > > Judging from a quick check we don't seem to have any such cases > > currently so this could be implemented as a submission failure rather > > than another warning. > > All right; I'll make the submission fail with a -EBADR (invalid request > descriptor) error; that seems like a good choice of an obscure and > otherwise unused value to match this case. But I'll put in a debugging > message, so that anyone who wants to know if this is occurring will have > a way to find out. Sounds good. Johan
Index: usb-devel/drivers/usb/core/urb.c =================================================================== --- usb-devel.orig/drivers/usb/core/urb.c +++ usb-devel/drivers/usb/core/urb.c @@ -407,6 +407,9 @@ int usb_submit_urb(struct urb *urb, gfp_ return -ENOEXEC; is_out = !(setup->bRequestType & USB_DIR_IN) || !setup->wLength; + dev_WARN_ONCE(&dev->dev, (usb_pipeout(urb->pipe) != is_out), + "BOGUS control dir, pipe %x doesn't match bRequestType %x\n", + urb->pipe, setup->bRequestType); } else { is_out = usb_endpoint_dir_out(&ep->desc); }
When a control URB is submitted, the direction indicated by URB's pipe member is supposed to match the direction indicated by the setup packet's bRequestType member. A mismatch could lead to trouble, depending on which field the host controller drivers use for determining the actual direction. This shouldn't ever happen; it would represent a careless bug in a kernel driver somewhere. This patch adds a dev_WARN_ONCE to let people know about the potential problem. Suggested-by: "Geoffrey D. Bennett" <g@b4.vu> Signed-off-by: Alan Stern <stern@rowland.harvard.edu> --- v2: Use dev_WARN_ONCE instead of dev_WARN [as1960b] drivers/usb/core/urb.c | 3 +++ 1 file changed, 3 insertions(+)