CVE-2024-36016 — tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

Affected: Linux, linux_kernel

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

tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

Assuming the following: - side A configures the n_gsm in basic option mode - side B sends the header of a basic option mode frame with data length 1 - side A switches to advanced option mode - side B sends 2 data bytes which exceeds gsm->len Reason: gsm->len is not used in advanced option mode. - side A switches to basic option mode - side B keeps sending until gsm0_receive() writes past gsm->buf Reason: Neither gsm->state nor gsm->len have been reset after reconfiguration.

Fix this by changing gsm->count to gsm->len comparison from equal to less than. Also add upper limit checks against the constant MAX_MRU in gsm0_receive() and gsm1_receive() to harden against memory corruption of gsm->len and gsm->mru.

All other checks remain as we still need to limit the data according to the user configuration and actual payload size.

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CVE-2024-36016 — tty: n_gsm: fix possible out-of-bounds in gsm0_receive()