[SRU][N/J/F][PATCH 0/1] CVE-2024-36016

[Bethany Jamison]

[Impact]

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.

[Fix]

Noble:	Clean cherry-pick from linux-6.8.y
Jammy:	Noble patch applied cleanly
Focal: 	Clean cherry-pick from linux-5.10.y
Bionic:	fix sent to esm ML
Xenial:	fix sent to esm ML
Trusty: not going to be fixed by us

[Test Case]

Compile and boot tested

[Where problems could occur]

This fix affects those who use the GSM 0710 tty multiplexor, an 
issue with this fix would be visible to the user via unexpected
system behavior or a system crash.

Daniel Starke (1):
  tty: n_gsm: fix possible out-of-bounds in gsm0_receive()

 drivers/tty/n_gsm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

-- 
2.34.1