From 3f3af97d8225a58ecdcde7217c030b17e5198226 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 5 Aug 2015 12:54:46 +0100 Subject: ASN.1: Fix actions on CHOICE elements with IMPLICIT tags In an ASN.1 description where there is a CHOICE construct that contains elements with IMPLICIT tags that refer to constructed types, actions to be taken on those elements should be conditional on the corresponding element actually being matched. Currently, however, such actions are performed unconditionally in the middle of processing the CHOICE. For example, look at elements 'b' and 'e' here: A ::= SEQUENCE { CHOICE { b [0] IMPLICIT B ({ do_XXXXXXXXXXXX_b }), c [1] EXPLICIT C ({ do_XXXXXXXXXXXX_c }), d [2] EXPLICIT B ({ do_XXXXXXXXXXXX_d }), e [3] IMPLICIT C ({ do_XXXXXXXXXXXX_e }), f [4] IMPLICIT INTEGER ({ do_XXXXXXXXXXXX_f }) } } ({ do_XXXXXXXXXXXX_A }) B ::= SET OF OBJECT IDENTIFIER ({ do_XXXXXXXXXXXX_oid }) C ::= SET OF INTEGER ({ do_XXXXXXXXXXXX_int }) They each have an action (do_XXXXXXXXXXXX_b and do_XXXXXXXXXXXX_e) that should only be processed if that element is matched. The problem is that there's no easy place to hang the action off in the subclause (type B for element 'b' and type C for element 'e') because subclause opcode sequences can be shared. To fix this, introduce a conditional action opcode(ASN1_OP_MAYBE_ACT) that the decoder only processes if the preceding match was successful. This can be seen in an excerpt from the output of the fixed ASN.1 compiler for the above ASN.1 description: [ 13] = ASN1_OP_COND_MATCH_JUMP_OR_SKIP, // e [ 14] = _tagn(CONT, CONS, 3), [ 15] = _jump_target(45), // --> C [ 16] = ASN1_OP_MAYBE_ACT, [ 17] = _action(ACT_do_XXXXXXXXXXXX_e), In this, if the op at [13] is matched (ie. element 'e' above) then the action at [16] will be performed. However, if the op at [13] doesn't match or is skipped because it is conditional and some previous op matched, then the action at [16] will be ignored. Note that to make this work in the decoder, the ASN1_OP_RETURN op must set the flag to indicate that a match happened. This is necessary because the _jump_target() seen above introduces a subclause (in this case an object of type 'C') which is likely to alter the flag. Setting the flag here is okay because to process a subclause, a match must have happened and caused a jump. This cannot be tested with the code as it stands, but rather affects future code. Signed-off-by: David Howells Reviewed-by: David Woodhouse --- lib/asn1_decoder.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'lib') diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c index 1a000bb050f9..55980d7e1ac0 100644 --- a/lib/asn1_decoder.c +++ b/lib/asn1_decoder.c @@ -33,6 +33,7 @@ static const unsigned char asn1_op_lengths[ASN1_OP__NR] = { [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, @@ -177,6 +178,7 @@ int asn1_ber_decoder(const struct asn1_decoder *decoder, 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. @@ -211,6 +213,7 @@ next_op: if ((op & ASN1_OP_MATCH__COND && flags & FLAG_MATCHED) || dp == datalen) { + flags &= ~FLAG_LAST_MATCHED; pc += asn1_op_lengths[op]; goto next_op; } @@ -422,8 +425,15 @@ next_op: 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; + } 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; @@ -431,6 +441,7 @@ next_op: if (unlikely(jsp <= 0)) goto jump_stack_underflow; pc = jump_stack[--jsp]; + flags |= FLAG_MATCHED | FLAG_LAST_MATCHED; goto next_op; default: @@ -438,7 +449,8 @@ next_op: } /* Shouldn't reach here */ - pr_err("ASN.1 decoder error: Found reserved opcode (%u)\n", op); + pr_err("ASN.1 decoder error: Found reserved opcode (%u) pc=%zu\n", + op, pc); return -EBADMSG; data_overrun_error: -- cgit v1.2.3 From 0d62e9dd6da45bbf0f33a8617afc5fe774c8f45f Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 5 Aug 2015 12:54:46 +0100 Subject: ASN.1: Fix non-match detection failure on data overrun If the ASN.1 decoder is asked to parse a sequence of objects, non-optional matches get skipped if there's no more data to be had rather than a data-overrun error being reported. This is due to the code segment that decides whether to skip optional matches (ie. matches that could get ignored because an element is marked OPTIONAL in the grammar) due to a lack of data also skips non-optional elements if the data pointer has reached the end of the buffer. This can be tested with the data decoder for the new RSA akcipher algorithm that takes three non-optional integers. Currently, it skips the last integer if there is insufficient data. Without the fix, #defining DEBUG in asn1_decoder.c will show something like: next_op: pc=0/13 dp=0/270 C=0 J=0 - match? 30 30 00 - TAG: 30 266 CONS next_op: pc=2/13 dp=4/270 C=1 J=0 - match? 02 02 00 - TAG: 02 257 - LEAF: 257 next_op: pc=5/13 dp=265/270 C=1 J=0 - match? 02 02 00 - TAG: 02 3 - LEAF: 3 next_op: pc=8/13 dp=270/270 C=1 J=0 next_op: pc=11/13 dp=270/270 C=1 J=0 - end cons t=4 dp=270 l=270/270 The next_op line for pc=8/13 should be followed by a match line. This is not exploitable for X.509 certificates by means of shortening the message and fixing up the ASN.1 CONS tags because: (1) The relevant records being built up are cleared before use. (2) If the message is shortened sufficiently to remove the public key, the ASN.1 parse of the RSA key will fail quickly due to a lack of data. (3) Extracted signature data is either turned into MPIs (which cope with a 0 length) or is simpler integers specifying algoritms and suchlike (which can validly be 0); and (4) The AKID and SKID extensions are optional and their removal is handled without risking passing a NULL to asymmetric_key_generate_id(). (5) If the certificate is truncated sufficiently to remove the subject, issuer or serialNumber then the ASN.1 decoder will fail with a 'Cons stack underflow' return. This is not exploitable for PKCS#7 messages by means of removal of elements from such a message from the tail end of a sequence: (1) Any shortened X.509 certs embedded in the PKCS#7 message are survivable as detailed above. (2) The message digest content isn't used if it shows a NULL pointer, similarly, the authattrs aren't used if that shows a NULL pointer. (3) A missing signature results in a NULL MPI - which the MPI routines deal with. (4) If data is NULL, it is expected that the message has detached content and that is handled appropriately. (5) If the serialNumber is excised, the unconditional action associated with it will pick up the containing SEQUENCE instead, so no NULL pointer will be seen here. If both the issuer and the serialNumber are excised, the ASN.1 decode will fail with an 'Unexpected tag' return. In either case, there's no way to get to asymmetric_key_generate_id() with a NULL pointer. (6) Other fields are decoded to simple integers. Shortening the message to omit an algorithm ID field will cause checks on this to fail early in the verification process. This can also be tested by snipping objects off of the end of the ASN.1 stream such that mandatory tags are removed - or even from the end of internal SEQUENCEs. If any mandatory tag is missing, the error EBADMSG *should* be produced. Without this patch ERANGE or ENOPKG might be produced or the parse may apparently succeed, perhaps with ENOKEY or EKEYREJECTED being produced later, depending on what gets snipped. Just snipping off the final BIT_STRING or OCTET_STRING from either sample should be a start since both are mandatory and neither will cause an EBADMSG without the patches Reported-by: Marcel Holtmann Signed-off-by: David Howells Tested-by: Marcel Holtmann Reviewed-by: David Woodhouse --- lib/asn1_decoder.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'lib') diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c index 55980d7e1ac0..3f74dd3e2910 100644 --- a/lib/asn1_decoder.c +++ b/lib/asn1_decoder.c @@ -210,9 +210,8 @@ next_op: unsigned char tmp; /* Skip conditional matches if possible */ - if ((op & ASN1_OP_MATCH__COND && - flags & FLAG_MATCHED) || - dp == datalen) { + 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; -- cgit v1.2.3 From 233ce79db4b23a174bcf30bde5d6ad913d5f46d3 Mon Sep 17 00:00:00 2001 From: David Howells Date: Wed, 5 Aug 2015 12:54:46 +0100 Subject: ASN.1: Handle 'ANY OPTIONAL' in grammar An ANY object in an ASN.1 grammar that is marked OPTIONAL should be skipped if there is no more data to be had. This can be tested by editing X.509 certificates or PKCS#7 messages to remove the NULL from subobjects that look like the following: SEQUENCE { OBJECT(2a864886f70d01010b); NULL(); } This is an algorithm identifier plus an optional parameter. The modified DER can be passed to one of: keyctl padd asymmetric "" @s Tested-by: Marcel Holtmann Reviewed-by: David Woodhouse --- include/linux/asn1_ber_bytecode.h | 17 +++++++++++------ lib/asn1_decoder.c | 8 ++++++++ scripts/asn1_compiler.c | 3 ++- 3 files changed, 21 insertions(+), 7 deletions(-) (limited to 'lib') diff --git a/include/linux/asn1_ber_bytecode.h b/include/linux/asn1_ber_bytecode.h index 27f35780aecf..ab3a6c002f7b 100644 --- a/include/linux/asn1_ber_bytecode.h +++ b/include/linux/asn1_ber_bytecode.h @@ -45,24 +45,27 @@ enum asn1_opcode { ASN1_OP_MATCH_JUMP = 0x04, ASN1_OP_MATCH_JUMP_OR_SKIP = 0x05, ASN1_OP_MATCH_ANY = 0x08, + ASN1_OP_MATCH_ANY_OR_SKIP = 0x09, ASN1_OP_MATCH_ANY_ACT = 0x0a, + ASN1_OP_MATCH_ANY_ACT_OR_SKIP = 0x0b, /* Everything before here matches unconditionally */ ASN1_OP_COND_MATCH_OR_SKIP = 0x11, ASN1_OP_COND_MATCH_ACT_OR_SKIP = 0x13, ASN1_OP_COND_MATCH_JUMP_OR_SKIP = 0x15, ASN1_OP_COND_MATCH_ANY = 0x18, + ASN1_OP_COND_MATCH_ANY_OR_SKIP = 0x19, ASN1_OP_COND_MATCH_ANY_ACT = 0x1a, + ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP = 0x1b, /* Everything before here will want a tag from the data */ -#define ASN1_OP__MATCHES_TAG ASN1_OP_COND_MATCH_ANY_ACT +#define ASN1_OP__MATCHES_TAG ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP /* These are here to help fill up space */ - ASN1_OP_COND_FAIL = 0x1b, - ASN1_OP_COMPLETE = 0x1c, - ASN1_OP_ACT = 0x1d, - ASN1_OP_MAYBE_ACT = 0x1e, - ASN1_OP_RETURN = 0x1f, + ASN1_OP_COND_FAIL = 0x1c, + ASN1_OP_COMPLETE = 0x1d, + ASN1_OP_ACT = 0x1e, + ASN1_OP_MAYBE_ACT = 0x1f, /* The following eight have bit 0 -> SET, 1 -> OF, 2 -> ACT */ ASN1_OP_END_SEQ = 0x20, @@ -77,6 +80,8 @@ enum asn1_opcode { #define ASN1_OP_END__OF 0x02 #define ASN1_OP_END__ACT 0x04 + ASN1_OP_RETURN = 0x28, + ASN1_OP__NR }; diff --git a/lib/asn1_decoder.c b/lib/asn1_decoder.c index 3f74dd3e2910..2b3f46c049d4 100644 --- a/lib/asn1_decoder.c +++ b/lib/asn1_decoder.c @@ -24,12 +24,16 @@ static const unsigned char asn1_op_lengths[ASN1_OP__NR] = { [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, @@ -304,7 +308,9 @@ next_op: /* Decide how to handle the operation */ switch (op) { case ASN1_OP_MATCH_ANY_ACT: + case ASN1_OP_MATCH_ANY_ACT_OR_SKIP: case ASN1_OP_COND_MATCH_ANY_ACT: + case ASN1_OP_COND_MATCH_ANY_ACT_OR_SKIP: ret = actions[machine[pc + 1]](context, hdr, tag, data + dp, len); if (ret < 0) return ret; @@ -321,8 +327,10 @@ next_op: case ASN1_OP_MATCH: case ASN1_OP_MATCH_OR_SKIP: case ASN1_OP_MATCH_ANY: + case ASN1_OP_MATCH_ANY_OR_SKIP: case ASN1_OP_COND_MATCH_OR_SKIP: case ASN1_OP_COND_MATCH_ANY: + case ASN1_OP_COND_MATCH_ANY_OR_SKIP: skip_data: if (!(flags & FLAG_CONS)) { if (flags & FLAG_INDEFINITE_LENGTH) { diff --git a/scripts/asn1_compiler.c b/scripts/asn1_compiler.c index 0515bced929a..1c75e22b6385 100644 --- a/scripts/asn1_compiler.c +++ b/scripts/asn1_compiler.c @@ -1401,7 +1401,8 @@ static void render_element(FILE *out, struct element *e, struct element *tag) act = e->action ? "_ACT" : ""; switch (e->compound) { case ANY: - render_opcode(out, "ASN1_OP_%sMATCH_ANY%s,", cond, act); + render_opcode(out, "ASN1_OP_%sMATCH_ANY%s%s,", + cond, act, skippable ? "_OR_SKIP" : ""); if (e->name) render_more(out, "\t\t// %*.*s", (int)e->name->size, (int)e->name->size, -- cgit v1.2.3