From: Daniel Starke <[email protected]>
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: [email protected]
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218708
Tested-by: [email protected]
Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: [email protected]
Signed-off-by: Daniel Starke <[email protected]>
---
drivers/tty/n_gsm.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index f5b0d91d32a7..7c697dab6f84 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
--
2.34.1
From: Daniel Starke <[email protected]>
The current implementation uses either gsm0_receive() or gsm1_receive()
depending on whether the user configured the mux in basic or advanced
option mode. Both functions share some state values over the same logical
elements of the frame. However, both frame types differ in their nature.
gsm0_receive() uses non-transparency framing, whereas gsm1_receive() uses
transparency mechanism. Switching between both modes leaves the receive
function in an undefined state when done during frame reception.
Fix this by splitting both states. Add gsm0_receive_state_check_and_fix()
and gsm1_receive_state_check_and_fix() to ensure that gsm->state is reset
after a change of gsm->receive.
Note that gsm->state is only accessed in:
- gsm0_receive()
- gsm1_receive()
- gsm_error()
Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: [email protected]
Signed-off-by: Daniel Starke <[email protected]>
---
drivers/tty/n_gsm.c | 133 ++++++++++++++++++++++++++++++--------------
1 file changed, 92 insertions(+), 41 deletions(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 7c697dab6f84..be35f7334ecd 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -245,16 +245,18 @@ enum gsm_encoding {
enum gsm_mux_state {
GSM_SEARCH,
- GSM_START,
- GSM_ADDRESS,
- GSM_CONTROL,
- GSM_LEN,
- GSM_DATA,
- GSM_FCS,
- GSM_OVERRUN,
- GSM_LEN0,
- GSM_LEN1,
- GSM_SSOF,
+ GSM0_ADDRESS,
+ GSM0_CONTROL,
+ GSM0_LEN0,
+ GSM0_LEN1,
+ GSM0_DATA,
+ GSM0_FCS,
+ GSM0_SSOF,
+ GSM1_START,
+ GSM1_ADDRESS,
+ GSM1_CONTROL,
+ GSM1_DATA,
+ GSM1_OVERRUN,
};
/*
@@ -2847,6 +2849,30 @@ static void gsm_queue(struct gsm_mux *gsm)
return;
}
+/**
+ * gsm0_receive_state_check_and_fix - check and correct receive state
+ * @gsm: gsm data for this ldisc instance
+ *
+ * Ensures that the current receive state is valid for basic option mode.
+ */
+
+static void gsm0_receive_state_check_and_fix(struct gsm_mux *gsm)
+{
+ switch (gsm->state) {
+ case GSM_SEARCH:
+ case GSM0_ADDRESS:
+ case GSM0_CONTROL:
+ case GSM0_LEN0:
+ case GSM0_LEN1:
+ case GSM0_DATA:
+ case GSM0_FCS:
+ case GSM0_SSOF:
+ break;
+ default:
+ gsm->state = GSM_SEARCH;
+ break;
+ }
+}
/**
* gsm0_receive - perform processing for non-transparency
@@ -2860,26 +2886,27 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
{
unsigned int len;
+ gsm0_receive_state_check_and_fix(gsm);
switch (gsm->state) {
case GSM_SEARCH: /* SOF marker */
if (c == GSM0_SOF) {
- gsm->state = GSM_ADDRESS;
+ gsm->state = GSM0_ADDRESS;
gsm->address = 0;
gsm->len = 0;
gsm->fcs = INIT_FCS;
}
break;
- case GSM_ADDRESS: /* Address EA */
+ case GSM0_ADDRESS: /* Address EA */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
if (gsm_read_ea(&gsm->address, c))
- gsm->state = GSM_CONTROL;
+ gsm->state = GSM0_CONTROL;
break;
- case GSM_CONTROL: /* Control Byte */
+ case GSM0_CONTROL: /* Control Byte */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
gsm->control = c;
- gsm->state = GSM_LEN0;
+ gsm->state = GSM0_LEN0;
break;
- case GSM_LEN0: /* Length EA */
+ case GSM0_LEN0: /* Length EA */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
if (gsm_read_ea(&gsm->len, c)) {
if (gsm->len > gsm->mru) {
@@ -2889,14 +2916,14 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
}
gsm->count = 0;
if (!gsm->len)
- gsm->state = GSM_FCS;
+ gsm->state = GSM0_FCS;
else
- gsm->state = GSM_DATA;
+ gsm->state = GSM0_DATA;
break;
}
- gsm->state = GSM_LEN1;
+ gsm->state = GSM0_LEN1;
break;
- case GSM_LEN1:
+ case GSM0_LEN1:
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
len = c;
gsm->len |= len << 7;
@@ -2907,11 +2934,11 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
}
gsm->count = 0;
if (!gsm->len)
- gsm->state = GSM_FCS;
+ gsm->state = GSM0_FCS;
else
- gsm->state = GSM_DATA;
+ gsm->state = GSM0_DATA;
break;
- case GSM_DATA: /* Data */
+ case GSM0_DATA: /* Data */
gsm->buf[gsm->count++] = c;
if (gsm->count >= MAX_MRU) {
gsm->bad_size++;
@@ -2922,14 +2949,14 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
gsm->fcs = gsm_fcs_add_block(gsm->fcs, gsm->buf,
gsm->count);
}
- gsm->state = GSM_FCS;
+ gsm->state = GSM0_FCS;
}
break;
- case GSM_FCS: /* FCS follows the packet */
+ case GSM0_FCS: /* FCS follows the packet */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
- gsm->state = GSM_SSOF;
+ gsm->state = GSM0_SSOF;
break;
- case GSM_SSOF:
+ case GSM0_SSOF:
gsm->state = GSM_SEARCH;
if (c == GSM0_SOF)
gsm_queue(gsm);
@@ -2942,6 +2969,29 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
}
}
+/**
+ * gsm1_receive_state_check_and_fix - check and correct receive state
+ * @gsm: gsm data for this ldisc instance
+ *
+ * Ensures that the current receive state is valid for advanced option mode.
+ */
+
+static void gsm1_receive_state_check_and_fix(struct gsm_mux *gsm)
+{
+ switch (gsm->state) {
+ case GSM_SEARCH:
+ case GSM1_START:
+ case GSM1_ADDRESS:
+ case GSM1_CONTROL:
+ case GSM1_DATA:
+ case GSM1_OVERRUN:
+ break;
+ default:
+ gsm->state = GSM_SEARCH;
+ break;
+ }
+}
+
/**
* gsm1_receive - perform processing for non-transparency
* @gsm: gsm data for this ldisc instance
@@ -2952,6 +3002,7 @@ static void gsm0_receive(struct gsm_mux *gsm, u8 c)
static void gsm1_receive(struct gsm_mux *gsm, u8 c)
{
+ gsm1_receive_state_check_and_fix(gsm);
/* handle XON/XOFF */
if ((c & ISO_IEC_646_MASK) == XON) {
gsm->constipated = true;
@@ -2964,11 +3015,11 @@ static void gsm1_receive(struct gsm_mux *gsm, u8 c)
}
if (c == GSM1_SOF) {
/* EOF is only valid in frame if we have got to the data state */
- if (gsm->state == GSM_DATA) {
+ if (gsm->state == GSM1_DATA) {
if (gsm->count < 1) {
/* Missing FSC */
gsm->malformed++;
- gsm->state = GSM_START;
+ gsm->state = GSM1_START;
return;
}
/* Remove the FCS from data */
@@ -2984,14 +3035,14 @@ static void gsm1_receive(struct gsm_mux *gsm, u8 c)
gsm->fcs = gsm_fcs_add(gsm->fcs, gsm->buf[gsm->count]);
gsm->len = gsm->count;
gsm_queue(gsm);
- gsm->state = GSM_START;
+ gsm->state = GSM1_START;
return;
}
/* Any partial frame was a runt so go back to start */
- if (gsm->state != GSM_START) {
+ if (gsm->state != GSM1_START) {
if (gsm->state != GSM_SEARCH)
gsm->malformed++;
- gsm->state = GSM_START;
+ gsm->state = GSM1_START;
}
/* A SOF in GSM_START means we are still reading idling or
framing bytes */
@@ -3012,30 +3063,30 @@ static void gsm1_receive(struct gsm_mux *gsm, u8 c)
gsm->escape = false;
}
switch (gsm->state) {
- case GSM_START: /* First byte after SOF */
+ case GSM1_START: /* First byte after SOF */
gsm->address = 0;
- gsm->state = GSM_ADDRESS;
+ gsm->state = GSM1_ADDRESS;
gsm->fcs = INIT_FCS;
fallthrough;
- case GSM_ADDRESS: /* Address continuation */
+ case GSM1_ADDRESS: /* Address continuation */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
if (gsm_read_ea(&gsm->address, c))
- gsm->state = GSM_CONTROL;
+ gsm->state = GSM1_CONTROL;
break;
- case GSM_CONTROL: /* Control Byte */
+ case GSM1_CONTROL: /* Control Byte */
gsm->fcs = gsm_fcs_add(gsm->fcs, c);
gsm->control = c;
gsm->count = 0;
- gsm->state = GSM_DATA;
+ gsm->state = GSM1_DATA;
break;
- case GSM_DATA: /* Data */
+ case GSM1_DATA: /* Data */
if (gsm->count > gsm->mru || gsm->count > MAX_MRU) { /* Allow one for the FCS */
- gsm->state = GSM_OVERRUN;
+ gsm->state = GSM1_OVERRUN;
gsm->bad_size++;
} else
gsm->buf[gsm->count++] = c;
break;
- case GSM_OVERRUN: /* Over-long - eg a dropped SOF */
+ case GSM1_OVERRUN: /* Over-long - eg a dropped SOF */
break;
default:
pr_debug("%s: unhandled state: %d\n", __func__, gsm->state);
--
2.34.1