More robust bounds checking on llc pdu parsing

We now have a list containing the lengths of the different llc pdu type minimum lengths
Before parsing the pdu, we validate the l2len is indeed sufficient to contain the pdu
This prevents out-of-bounds reads for corrupted packets.

Change-Id: I118ba2227a22afd295fffaa51aab3e45e85ff3d7
master
wbokslag 4 months ago
parent 372b1b272c
commit 615146270f
  1. 57
      src/tetra_llc_pdu.c

@ -82,6 +82,25 @@ const char *tetra_get_llc_pdut_dec_name(enum tllc_pdut_dec pdut)
return get_value_string(pdut_dec_names, pdut);
}
static const uint8_t tetra_llc_pdu_lengths[16] = {
6, /* TLLC_PDUT_BL_ADATA */
5, /* TLLC_PDUT_BL_DATA */
4, /* TLLC_PDUT_BL_UDATA */
5, /* TLLC_PDUT_BL_ACK */
6 + 32, /* TLLC_PDUT_BL_ADATA_FCS */
5 + 32, /* TLLC_PDUT_BL_DATA_FCS */
4 + 32, /* TLLC_PDUT_BL_UDATA_FCS */
5 + 32, /* TLLC_PDUT_BL_ACK_FCS */
0, /* Not implemented, TLLC_PDUT_AL_SETUP */
13, /* TLLC_PDUT_AL_DATA_FINAL */
17, /* TLLC_PDUT_AL_UDATA_UFINAL */
1, /* Not implemented, TLLC_PDUT_AL_ACK_RNR */
0, /* Not implemented, TLLC_PDUT_AL_RECONNECT */
0, /* Not implemented, TLLC_PDUT_SUPPL */
0, /* Not implemented, TLLC_PDUT_L2SIG */
0, /* Not implemented, TLLD_PDUT_AL_DISC */
};
static uint32_t tetra_llc_compute_fcs(const uint8_t *buf, int len)
{
uint32_t crc = 0xFFFFFFFF;
@ -99,7 +118,7 @@ static uint32_t tetra_llc_compute_fcs(const uint8_t *buf, int len)
return ~crc;
}
static int tetra_llc_check_fcs(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
static bool tetra_llc_check_fcs(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
{
uint32_t computed_fcs = tetra_llc_compute_fcs(buf, len);
return lpp->fcs == computed_fcs;
@ -110,12 +129,19 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
uint8_t *cur = buf;
uint8_t pdu_type;
lpp->have_fcs = 0;
lpp->have_fcs = false;
lpp->fcs = 0;
lpp->fcs_invalid = 0;
lpp->fcs_invalid = false;
pdu_type = bits_to_uint(cur, 4);
cur += 4;
/* Check length to prevent out of bounds reads */
if (len < tetra_llc_pdu_lengths[pdu_type]) {
printf("WARNING llc pdu too small to parse, needed %d\n", tetra_llc_pdu_lengths[pdu_type]);
lpp->tl_sdu_len = 0;
return len;
}
switch (pdu_type) {
case TLLC_PDUT_BL_ADATA:
@ -127,12 +153,8 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
lpp->pdu_type = TLLC_PDUT_DEC_BL_ADATA;
if (pdu_type == TLLC_PDUT_BL_ADATA_FCS) {
if (lpp->tl_sdu_len < 32) {
printf("\nWARNING frame too small for FCS (%d)\n", lpp->tl_sdu_len);
goto out;
}
lpp->tl_sdu_len -= 32;
lpp->have_fcs = 1;
lpp->have_fcs = true;
lpp->fcs = bits_to_uint(buf + len - 32, 32);
lpp->fcs_invalid = !tetra_llc_check_fcs(lpp, cur, lpp->tl_sdu_len);
}
@ -146,12 +168,8 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
lpp->pdu_type = TLLC_PDUT_DEC_BL_DATA;
if (pdu_type == TLLC_PDUT_BL_DATA_FCS) {
if (lpp->tl_sdu_len < 32) {
printf("\nWARNING frame too small for FCS (%d)\n", lpp->tl_sdu_len);
goto out;
}
lpp->tl_sdu_len -= 32;
lpp->have_fcs = 1;
lpp->have_fcs = true;
lpp->fcs = bits_to_uint(buf + len - 32, 32);
lpp->fcs_invalid = !tetra_llc_check_fcs(lpp, cur, lpp->tl_sdu_len);
}
@ -164,12 +182,8 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
lpp->pdu_type = TLLC_PDUT_DEC_BL_UDATA;
if (pdu_type == TLLC_PDUT_BL_UDATA_FCS) {
if (lpp->tl_sdu_len < 32) {
printf("\nWARNING frame too small for FCS (%d)\n", lpp->tl_sdu_len);
goto out;
}
lpp->tl_sdu_len -= 32;
lpp->have_fcs = 1;
lpp->have_fcs = true;
lpp->fcs = bits_to_uint(buf + len - 32, 32);
lpp->fcs_invalid = !tetra_llc_check_fcs(lpp, cur, lpp->tl_sdu_len);
}
@ -183,12 +197,8 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
lpp->pdu_type = TLLC_PDUT_DEC_BL_ACK;
if (pdu_type == TLLC_PDUT_BL_ACK_FCS) {
if (lpp->tl_sdu_len < 32) {
printf("\nWARNING frame too small for FCS (%d)\n", lpp->tl_sdu_len);
goto out;
}
lpp->tl_sdu_len -= 32;
lpp->have_fcs = 1;
lpp->have_fcs = true;
lpp->fcs = bits_to_uint(buf + len - 32, 32);
lpp->fcs_invalid = !tetra_llc_check_fcs(lpp, cur, lpp->tl_sdu_len);
}
@ -286,7 +296,6 @@ int tetra_llc_pdu_parse(struct tetra_llc_pdu *lpp, uint8_t *buf, int len)
lpp->tl_sdu_len = 0;
}
out:
/* Sanity check to prevent (further) out of bounds reads */
if (len < cur - buf) {
lpp->tl_sdu_len = 0;

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