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

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commit 47388e807f85948eefc403a8a5fdc5b406a65d5a upstream.

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.

Reported-by: j51569436@gmail.com
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218708
Tested-by: j51569436@gmail.com
Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20240424054842.7741-1-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Starke 2024-04-24 07:48:41 +02:00 committed by Ksawlii
parent 6dbf6f0129
commit 5c838410ee
1 changed files with 6 additions and 2 deletions
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8
drivers/tty/n_gsm.c
View file

@ -2082,8 +2082,12 @@ static void gsm0_receive(struct gsm_mux *gsm, unsigned char c)
break;
case GSM_DATA: /* Data */
gsm->buf[gsm->count++] = c;
if (gsm->count == gsm->len)
if (gsm->count >= MAX_MRU) {
gsm->bad_size++;
gsm->state = GSM_SEARCH;
} else if (gsm->count >= gsm->len) {
gsm->state = GSM_FCS;
}
break;
case GSM_FCS: /* FCS follows the packet */
gsm->received_fcs = c;
@ -2176,7 +2180,7 @@ static void gsm1_receive(struct gsm_mux *gsm, unsigned char c)
gsm->state = GSM_DATA;
break;
case GSM_DATA: /* Data */
if (gsm->count > gsm->mru) { /* Allow one for the FCS */
if (gsm->count > gsm->mru || gsm->count > MAX_MRU) { /* Allow one for the FCS */
gsm->state = GSM_OVERRUN;
gsm->bad_size++;
} else