diff options
Diffstat (limited to 'lib/asn1_decoder.c')
| -rw-r--r-- | lib/asn1_decoder.c | 521 |
1 files changed, 521 insertions, 0 deletions
diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c new file mode 100644 index 0000000000..13da529e2e --- /dev/null +++ b/lib/asn1_decoder.c @@ -0,0 +1,521 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Decoder for ASN.1 BER/DER/CER encoded bytestream + * + * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#include <linux/export.h> +#include <linux/kernel.h> +#include <linux/errno.h> +#include <linux/module.h> +#include <linux/asn1_decoder.h> +#include <linux/asn1_ber_bytecode.h> + +static const unsigned char asn1_op_lengths[ASN1_OP__NR] = { + /* OPC TAG JMP ACT */ + [ASN1_OP_MATCH] = 1 + 1, + [ASN1_OP_MATCH_OR_SKIP] = 1 + 1, + [ASN1_OP_MATCH_ACT] = 1 + 1 + 1, + [ASN1_OP_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, + [ASN1_OP_MATCH_JUMP] = 1 + 1 + 1, + [ASN1_OP_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, + [ASN1_OP_MATCH_ANY] = 1, + [ASN1_OP_MATCH_ANY_OR_SKIP] = 1, + [ASN1_OP_MATCH_ANY_ACT] = 1 + 1, + [ASN1_OP_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, + [ASN1_OP_COND_MATCH_OR_SKIP] = 1 + 1, + [ASN1_OP_COND_MATCH_ACT_OR_SKIP] = 1 + 1 + 1, + [ASN1_OP_COND_MATCH_JUMP_OR_SKIP] = 1 + 1 + 1, + [ASN1_OP_COND_MATCH_ANY] = 1, + [ASN1_OP_COND_MATCH_ANY_OR_SKIP] = 1, + [ASN1_OP_COND_MATCH_ANY_ACT] = 1 + 1, + [ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP] = 1 + 1, + [ASN1_OP_COND_FAIL] = 1, + [ASN1_OP_COMPLETE] = 1, + [ASN1_OP_ACT] = 1 + 1, + [ASN1_OP_MAYBE_ACT] = 1 + 1, + [ASN1_OP_RETURN] = 1, + [ASN1_OP_END_SEQ] = 1, + [ASN1_OP_END_SEQ_OF] = 1 + 1, + [ASN1_OP_END_SET] = 1, + [ASN1_OP_END_SET_OF] = 1 + 1, + [ASN1_OP_END_SEQ_ACT] = 1 + 1, + [ASN1_OP_END_SEQ_OF_ACT] = 1 + 1 + 1, + [ASN1_OP_END_SET_ACT] = 1 + 1, + [ASN1_OP_END_SET_OF_ACT] = 1 + 1 + 1, +}; + +/* + * Find the length of an indefinite length object + * @data: The data buffer + * @datalen: The end of the innermost containing element in the buffer + * @_dp: The data parse cursor (updated before returning) + * @_len: Where to return the size of the element. + * @_errmsg: Where to return a pointer to an error message on error + */ +static int asn1_find_indefinite_length(const unsigned char *data, size_t datalen, + size_t *_dp, size_t *_len, + const char **_errmsg) +{ + unsigned char tag, tmp; + size_t dp = *_dp, len, n; + int indef_level = 1; + +next_tag: + if (unlikely(datalen - dp < 2)) { + if (datalen == dp) + goto missing_eoc; + goto data_overrun_error; + } + + /* Extract a tag from the data */ + tag = data[dp++]; + if (tag == ASN1_EOC) { + /* It appears to be an EOC. */ + if (data[dp++] != 0) + goto invalid_eoc; + if (--indef_level <= 0) { + *_len = dp - *_dp; + *_dp = dp; + return 0; + } + goto next_tag; + } + + if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) { + do { + if (unlikely(datalen - dp < 2)) + goto data_overrun_error; + tmp = data[dp++]; + } while (tmp & 0x80); + } + + /* Extract the length */ + len = data[dp++]; + if (len <= 0x7f) + goto check_length; + + if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { + /* Indefinite length */ + if (unlikely((tag & ASN1_CONS_BIT) == ASN1_PRIM << 5)) + goto indefinite_len_primitive; + indef_level++; + goto next_tag; + } + + n = len - 0x80; + if (unlikely(n > sizeof(len) - 1)) + goto length_too_long; + if (unlikely(n > datalen - dp)) + goto data_overrun_error; + len = 0; + for (; n > 0; n--) { + len <<= 8; + len |= data[dp++]; + } +check_length: + if (len > datalen - dp) + goto data_overrun_error; + dp += len; + goto next_tag; + +length_too_long: + *_errmsg = "Unsupported length"; + goto error; +indefinite_len_primitive: + *_errmsg = "Indefinite len primitive not permitted"; + goto error; +invalid_eoc: + *_errmsg = "Invalid length EOC"; + goto error; +data_overrun_error: + *_errmsg = "Data overrun error"; + goto error; +missing_eoc: + *_errmsg = "Missing EOC in indefinite len cons"; +error: + *_dp = dp; + return -1; +} + +/** + * asn1_ber_decoder - Decoder BER/DER/CER ASN.1 according to pattern + * @decoder: The decoder definition (produced by asn1_compiler) + * @context: The caller's context (to be passed to the action functions) + * @data: The encoded data + * @datalen: The size of the encoded data + * + * Decode BER/DER/CER encoded ASN.1 data according to a bytecode pattern + * produced by asn1_compiler. Action functions are called on marked tags to + * allow the caller to retrieve significant data. + * + * LIMITATIONS: + * + * To keep down the amount of stack used by this function, the following limits + * have been imposed: + * + * (1) This won't handle datalen > 65535 without increasing the size of the + * cons stack elements and length_too_long checking. + * + * (2) The stack of constructed types is 10 deep. If the depth of non-leaf + * constructed types exceeds this, the decode will fail. + * + * (3) The SET type (not the SET OF type) isn't really supported as tracking + * what members of the set have been seen is a pain. + */ +int asn1_ber_decoder(const struct asn1_decoder *decoder, + void *context, + const unsigned char *data, + size_t datalen) +{ + const unsigned char *machine = decoder->machine; + const asn1_action_t *actions = decoder->actions; + size_t machlen = decoder->machlen; + enum asn1_opcode op; + unsigned char tag = 0, csp = 0, jsp = 0, optag = 0, hdr = 0; + const char *errmsg; + size_t pc = 0, dp = 0, tdp = 0, len = 0; + int ret; + + unsigned char flags = 0; +#define FLAG_INDEFINITE_LENGTH 0x01 +#define FLAG_MATCHED 0x02 +#define FLAG_LAST_MATCHED 0x04 /* Last tag matched */ +#define FLAG_CONS 0x20 /* Corresponds to CONS bit in the opcode tag + * - ie. whether or not we are going to parse + * a compound type. + */ + +#define NR_CONS_STACK 10 + unsigned short cons_dp_stack[NR_CONS_STACK]; + unsigned short cons_datalen_stack[NR_CONS_STACK]; + unsigned char cons_hdrlen_stack[NR_CONS_STACK]; +#define NR_JUMP_STACK 10 + unsigned char jump_stack[NR_JUMP_STACK]; + + if (datalen > 65535) + return -EMSGSIZE; + +next_op: + pr_debug("next_op: pc=\e[32m%zu\e[m/%zu dp=\e[33m%zu\e[m/%zu C=%d J=%d\n", + pc, machlen, dp, datalen, csp, jsp); + if (unlikely(pc >= machlen)) + goto machine_overrun_error; + op = machine[pc]; + if (unlikely(pc + asn1_op_lengths[op] > machlen)) + goto machine_overrun_error; + + /* If this command is meant to match a tag, then do that before + * evaluating the command. + */ + if (op <= ASN1_OP__MATCHES_TAG) { + unsigned char tmp; + + /* Skip conditional matches if possible */ + if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) || + (op & ASN1_OP_MATCH__SKIP && dp == datalen)) { + flags &= ~FLAG_LAST_MATCHED; + pc += asn1_op_lengths[op]; + goto next_op; + } + + flags = 0; + hdr = 2; + + /* Extract a tag from the data */ + if (unlikely(datalen - dp < 2)) + goto data_overrun_error; + tag = data[dp++]; + if (unlikely((tag & 0x1f) == ASN1_LONG_TAG)) + goto long_tag_not_supported; + + if (op & ASN1_OP_MATCH__ANY) { + pr_debug("- any %02x\n", tag); + } else { + /* Extract the tag from the machine + * - Either CONS or PRIM are permitted in the data if + * CONS is not set in the op stream, otherwise CONS + * is mandatory. + */ + optag = machine[pc + 1]; + flags |= optag & FLAG_CONS; + + /* Determine whether the tag matched */ + tmp = optag ^ tag; + tmp &= ~(optag & ASN1_CONS_BIT); + pr_debug("- match? %02x %02x %02x\n", tag, optag, tmp); + if (tmp != 0) { + /* All odd-numbered tags are MATCH_OR_SKIP. */ + if (op & ASN1_OP_MATCH__SKIP) { + pc += asn1_op_lengths[op]; + dp--; + goto next_op; + } + goto tag_mismatch; + } + } + flags |= FLAG_MATCHED; + + len = data[dp++]; + if (len > 0x7f) { + if (unlikely(len == ASN1_INDEFINITE_LENGTH)) { + /* Indefinite length */ + if (unlikely(!(tag & ASN1_CONS_BIT))) + goto indefinite_len_primitive; + flags |= FLAG_INDEFINITE_LENGTH; + if (unlikely(2 > datalen - dp)) + goto data_overrun_error; + } else { + int n = len - 0x80; + if (unlikely(n > 2)) + goto length_too_long; + if (unlikely(n > datalen - dp)) + goto data_overrun_error; + hdr += n; + for (len = 0; n > 0; n--) { + len <<= 8; + len |= data[dp++]; + } + if (unlikely(len > datalen - dp)) + goto data_overrun_error; + } + } else { + if (unlikely(len > datalen - dp)) + goto data_overrun_error; + } + + if (flags & FLAG_CONS) { + /* For expected compound forms, we stack the positions + * of the start and end of the data. + */ + if (unlikely(csp >= NR_CONS_STACK)) + goto cons_stack_overflow; + cons_dp_stack[csp] = dp; + cons_hdrlen_stack[csp] = hdr; + if (!(flags & FLAG_INDEFINITE_LENGTH)) { + cons_datalen_stack[csp] = datalen; + datalen = dp + len; + } else { + cons_datalen_stack[csp] = 0; + } + csp++; + } + + pr_debug("- TAG: %02x %zu%s\n", + tag, len, flags & FLAG_CONS ? " CONS" : ""); + tdp = dp; + } + + /* Decide how to handle the operation */ + switch (op) { + case ASN1_OP_MATCH: + case ASN1_OP_MATCH_OR_SKIP: + case ASN1_OP_MATCH_ACT: + case ASN1_OP_MATCH_ACT_OR_SKIP: + case ASN1_OP_MATCH_ANY: + case ASN1_OP_MATCH_ANY_OR_SKIP: + case ASN1_OP_MATCH_ANY_ACT: + case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: + case ASN1_OP_COND_MATCH_OR_SKIP: + case ASN1_OP_COND_MATCH_ACT_OR_SKIP: + case ASN1_OP_COND_MATCH_ANY: + case ASN1_OP_COND_MATCH_ANY_OR_SKIP: + case ASN1_OP_COND_MATCH_ANY_ACT: + case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: + + if (!(flags & FLAG_CONS)) { + if (flags & FLAG_INDEFINITE_LENGTH) { + size_t tmp = dp; + + ret = asn1_find_indefinite_length( + data, datalen, &tmp, &len, &errmsg); + if (ret < 0) + goto error; + } + pr_debug("- LEAF: %zu\n", len); + } + + if (op & ASN1_OP_MATCH__ACT) { + unsigned char act; + + if (op & ASN1_OP_MATCH__ANY) + act = machine[pc + 1]; + else + act = machine[pc + 2]; + ret = actions[act](context, hdr, tag, data + dp, len); + if (ret < 0) + return ret; + } + + if (!(flags & FLAG_CONS)) + dp += len; + pc += asn1_op_lengths[op]; + goto next_op; + + case ASN1_OP_MATCH_JUMP: + case ASN1_OP_MATCH_JUMP_OR_SKIP: + case ASN1_OP_COND_MATCH_JUMP_OR_SKIP: + pr_debug("- MATCH_JUMP\n"); + if (unlikely(jsp == NR_JUMP_STACK)) + goto jump_stack_overflow; + jump_stack[jsp++] = pc + asn1_op_lengths[op]; + pc = machine[pc + 2]; + goto next_op; + + case ASN1_OP_COND_FAIL: + if (unlikely(!(flags & FLAG_MATCHED))) + goto tag_mismatch; + pc += asn1_op_lengths[op]; + goto next_op; + + case ASN1_OP_COMPLETE: + if (unlikely(jsp != 0 || csp != 0)) { + pr_err("ASN.1 decoder error: Stacks not empty at completion (%u, %u)\n", + jsp, csp); + return -EBADMSG; + } + return 0; + + case ASN1_OP_END_SET: + case ASN1_OP_END_SET_ACT: + if (unlikely(!(flags & FLAG_MATCHED))) + goto tag_mismatch; + fallthrough; + + case ASN1_OP_END_SEQ: + case ASN1_OP_END_SET_OF: + case ASN1_OP_END_SEQ_OF: + case ASN1_OP_END_SEQ_ACT: + case ASN1_OP_END_SET_OF_ACT: + case ASN1_OP_END_SEQ_OF_ACT: + if (unlikely(csp <= 0)) + goto cons_stack_underflow; + csp--; + tdp = cons_dp_stack[csp]; + hdr = cons_hdrlen_stack[csp]; + len = datalen; + datalen = cons_datalen_stack[csp]; + pr_debug("- end cons t=%zu dp=%zu l=%zu/%zu\n", + tdp, dp, len, datalen); + if (datalen == 0) { + /* Indefinite length - check for the EOC. */ + datalen = len; + if (unlikely(datalen - dp < 2)) + goto data_overrun_error; + if (data[dp++] != 0) { + if (op & ASN1_OP_END__OF) { + dp--; + csp++; + pc = machine[pc + 1]; + pr_debug("- continue\n"); + goto next_op; + } + goto missing_eoc; + } + if (data[dp++] != 0) + goto invalid_eoc; + len = dp - tdp - 2; + } else { + if (dp < len && (op & ASN1_OP_END__OF)) { + datalen = len; + csp++; + pc = machine[pc + 1]; + pr_debug("- continue\n"); + goto next_op; + } + if (dp != len) + goto cons_length_error; + len -= tdp; + pr_debug("- cons len l=%zu d=%zu\n", len, dp - tdp); + } + + if (op & ASN1_OP_END__ACT) { + unsigned char act; + if (op & ASN1_OP_END__OF) + act = machine[pc + 2]; + else + act = machine[pc + 1]; + ret = actions[act](context, hdr, 0, data + tdp, len); + if (ret < 0) + return ret; + } + pc += asn1_op_lengths[op]; + goto next_op; + + case ASN1_OP_MAYBE_ACT: + if (!(flags & FLAG_LAST_MATCHED)) { + pc += asn1_op_lengths[op]; + goto next_op; + } + fallthrough; + + case ASN1_OP_ACT: + ret = actions[machine[pc + 1]](context, hdr, tag, data + tdp, len); + if (ret < 0) + return ret; + pc += asn1_op_lengths[op]; + goto next_op; + + case ASN1_OP_RETURN: + if (unlikely(jsp <= 0)) + goto jump_stack_underflow; + pc = jump_stack[--jsp]; + flags |= FLAG_MATCHED | FLAG_LAST_MATCHED; + goto next_op; + + default: + break; + } + + /* Shouldn't reach here */ + pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n", + op, pc); + return -EBADMSG; + +data_overrun_error: + errmsg = "Data overrun error"; + goto error; +machine_overrun_error: + errmsg = "Machine overrun error"; + goto error; +jump_stack_underflow: + errmsg = "Jump stack underflow"; + goto error; +jump_stack_overflow: + errmsg = "Jump stack overflow"; + goto error; +cons_stack_underflow: + errmsg = "Cons stack underflow"; + goto error; +cons_stack_overflow: + errmsg = "Cons stack overflow"; + goto error; +cons_length_error: + errmsg = "Cons length error"; + goto error; +missing_eoc: + errmsg = "Missing EOC in indefinite len cons"; + goto error; +invalid_eoc: + errmsg = "Invalid length EOC"; + goto error; +length_too_long: + errmsg = "Unsupported length"; + goto error; +indefinite_len_primitive: + errmsg = "Indefinite len primitive not permitted"; + goto error; +tag_mismatch: + errmsg = "Unexpected tag"; + goto error; +long_tag_not_supported: + errmsg = "Long tag not supported"; +error: + pr_debug("\nASN1: %s [m=%zu d=%zu ot=%02x t=%02x l=%zu]\n", + errmsg, pc, dp, optag, tag, len); + return -EBADMSG; +} +EXPORT_SYMBOL_GPL(asn1_ber_decoder); + +MODULE_LICENSE("GPL"); |