FAILED: patch "[PATCH] tty: n_gsm: fix possible out-of-bounds in gsm0_receive()" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 47388e807f85948eefc403a8a5fdc5b406a65d5a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024052539-pacific-rejoin-8bca@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 47388e807f85948eefc403a8a5fdc5b406a65d5a Mon Sep 17 00:00:00 2001
From: Daniel Starke <daniel.starke@siemens.com>
Date: Wed, 24 Apr 2024 07:48:41 +0200
Subject: [PATCH] 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.

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>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 4036566febcb..72b82bf1c280 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2913,7 +2913,10 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 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) {
 			/* Calculate final FCS for UI frames over all data */
 			if ((gsm->control & ~PF) != UIH) {
 				gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf,
@@ -3026,7 +3029,7 @@ static void gsm1_receive(struct gsm_mux *gsm, u8 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