tty: n_gsm: fix possible out-of-bounds in gsm0_receive()
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>
(cherry picked from commit 9513d4148950b05bc99fa7314dc883cc0e1605e5)
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index a60d4b5..f7c8b0f 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1986,8 +1986,12 @@
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;
@@ -2067,7 +2071,7 @@
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