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authorDavid Howells <dhowells@redhat.com>2015-08-05 12:54:46 +0100
committerDavid Howells <dhowells@redhat.com>2015-08-05 12:54:46 +0100
commit3f3af97d8225a58ecdcde7217c030b17e5198226 (patch)
tree2d229cf5aa9309eb3ab74018c438da93d3942ab0 /lib/asn1_decoder.c
parent8d9b21dcfe6814c92c9f445a7c742b7bab4f86b8 (diff)
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 <dhowells@redhat.com> Reviewed-by: David Woodhouse <David.Woodhouse@intel.com>
Diffstat (limited to 'lib/asn1_decoder.c')
-rw-r--r--lib/asn1_decoder.c14
1 files changed, 13 insertions, 1 deletions
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: