[Bug 528753] [NEW] snd_usb_audio - NULL pointer dereference in usb_ifnum_to_if+0x18/0x50

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Please note I don’t have direct access to the computer (HP Pavilion
dv5000), as it’s some 10 000 km away from me :)

That said, the problem is with Ubuntu Desktop Karmic, with kernels
ranging from 2.6.31.15 to 2.6.31.19; they all exhibit the same behavior
due to a slightly worn out USB socket, which makes the webcam USB plug
connect and reconnect all of sudden and very quickly.

Please note that the webcam is a Logitech Webcam C200, which includes a
sound device (mic in). This USB sound device seems to be the actual
cause of the oops, not the video device (uvcvideo). In fact, when using
an external microphone along with the sole video from the webcam, the
above mentioned disconnection only causes a loss of video, but
reactivating it (in the worst case, after replugging the webcam) always
gets the video back working. When the audio device is also used,
instead... keep on reading.

Actual results:
If the sudden disconnection happens while a program (e.g. Skype) is reading from the webcam, the kernel goes oops (see attached dmesg), and the following symptoms ensue:
· the webcam won’t work anymore
· anything sound-related won’t work either
· trying to start System > Preferences > Sound will hang with a message “Waiting for sound system to respond”
· closing Skype won’t work
· System Monitor won’t start, and trying to run “ps aux” will cause the terminal to hang
· trying to reboot will hang indefinitely at some point after shutting down X (so on some init.d script), requiring forced power off

Expected results:
Programs using the webcam might crash, freeze, stop reading from the webcam, but the kernel should stay stable and the remedy should be to just reinsert the USB plug and reactivate the video in the program.


The dmesg was taken with kernel 2.6.31.17, but the remaining files are from 2.6.31.15 (which seems to be more stable with hibernation). I hope that’s not a big deal. Also, the dmesg is partial, since it had to be sent via the Skype chat window, that’s not exactly designed for this purpose :) I hope I got all the relevant parts, though.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete

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snd_usb_audio - NULL pointer dereference in usb_ifnum_to_if+0x18/0x50
https://bugs.edge.launchpad.net/bugs/528753
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