4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Starke <daniel.starke@xxxxxxxxxxx> 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@xxxxxxxxx Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218708 Tested-by: j51569436@xxxxxxxxx Fixes: e1eaea46bb40 ("tty: n_gsm line discipline") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Daniel Starke <daniel.starke@xxxxxxxxxxx> Link: https://lore.kernel.org/r/20240424054842.7741-1-daniel.starke@xxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/n_gsm.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -1972,8 +1972,12 @@ static void gsm0_receive(struct gsm_mux 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; @@ -2053,7 +2057,7 @@ static void gsm1_receive(struct gsm_mux 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
