USB: cdc-acm: fix racy TIOCMIWAIT implementation

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Check the wakeup condition after adding the task to the waitqueue and
updating the task state to avoid missing a racing modem status update or
disconnect.

Store the old icount on entry and do not update it in the completion
handler to avoid missing events or reporting spurious ones (due to modem
status changes before TIOCMIWAIT was called).

Fixes: 5a6a62bdb9 ("cdc-acm: add TIOCMIWAIT")
Cc: stable <stable@kernel.org>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260907095130.130636-1-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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Johan Hovold 2026-09-07 11:51:30 +02:00 • committed by Greg Kroah-Hartman

parent 88c7e458af

commit be4219dd98

2 changed files with 19 additions and 18 deletions

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36

drivers/usb/class/cdc-acm.c

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1

drivers/usb/class/cdc-acm.h

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