Vulnerability CVE-2023-52872
Published: 2024-05-21

Description:
In the Linux kernel, the following vulnerability has been resolved:

tty: n_gsm: fix race condition in status line change on dead connections

gsm_cleanup_mux() cleans up the gsm by closing all DLCIs, stopping all
timers, removing the virtual tty devices and clearing the data queues.
This procedure, however, may cause subsequent changes of the virtual modem
status lines of a DLCI. More data is being added the outgoing data queue
and the deleted kick timer is restarted to handle this. At this point many
resources have already been removed by the cleanup procedure. Thus, a
kernel panic occurs.

Fix this by proving in gsm_modem_update() that the cleanup procedure has
not been started and the mux is still alive.

Note that writing to a virtual tty is already protected by checks against
the DLCI specific connection state.

 References:
https://git.kernel.org/stable/c/81a4dd5e6c78f5d8952fa8c9d36565db1fe01444
https://git.kernel.org/stable/c/df6cfab66ff2a44bd23ad5dd5309cb3421bb6593
https://git.kernel.org/stable/c/19d34b73234af542cc8a218cf398dee73cdb1890
https://git.kernel.org/stable/c/ce4df90333c4fe65acb8b5089fdfe9b955ce976a
https://git.kernel.org/stable/c/3a75b205de43365f80a33b98ec9289785da56243
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