]> git.stg.codes - stg.git/blobdiff - projects/stargazer/plugins/other/snmp/asn1/ber_decoder.c
SNMP Agent plugin added
[stg.git] / projects / stargazer / plugins / other / snmp / asn1 / ber_decoder.c
diff --git a/projects/stargazer/plugins/other/snmp/asn1/ber_decoder.c b/projects/stargazer/plugins/other/snmp/asn1/ber_decoder.c
new file mode 100644 (file)
index 0000000..601f66c
--- /dev/null
@@ -0,0 +1,283 @@
+/*-
+ * Copyright (c) 2003, 2004 Lev Walkin <vlm@lionet.info>. All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#include <asn_internal.h>
+
+#undef ADVANCE
+#define        ADVANCE(num_bytes)      do {                                    \
+               size_t num = num_bytes;                                 \
+               ptr = ((const char *)ptr) + num;                        \
+               size -= num;                                            \
+               consumed_myself += num;                                 \
+       } while(0)
+#undef RETURN
+#define        RETURN(_code)   do {                                            \
+               asn_dec_rval_t rval;                                    \
+               rval.code = _code;                                      \
+               if(opt_ctx) opt_ctx->step = step; /* Save context */    \
+               if(_code == RC_OK || opt_ctx)                           \
+                       rval.consumed = consumed_myself;                \
+               else                                                    \
+                       rval.consumed = 0;      /* Context-free */      \
+               return rval;                                            \
+       } while(0)
+
+/*
+ * The BER decoder of any type.
+ */
+asn_dec_rval_t
+ber_decode(asn_codec_ctx_t *opt_codec_ctx,
+       asn_TYPE_descriptor_t *type_descriptor,
+       void **struct_ptr, const void *ptr, size_t size) {
+       asn_codec_ctx_t s_codec_ctx;
+
+       /*
+        * Stack checker requires that the codec context
+        * must be allocated on the stack.
+        */
+       if(opt_codec_ctx) {
+               if(opt_codec_ctx->max_stack_size) {
+                       s_codec_ctx = *opt_codec_ctx;
+                       opt_codec_ctx = &s_codec_ctx;
+               }
+       } else {
+               /* If context is not given, be security-conscious anyway */
+               memset(&s_codec_ctx, 0, sizeof(s_codec_ctx));
+               s_codec_ctx.max_stack_size = _ASN_DEFAULT_STACK_MAX;
+               opt_codec_ctx = &s_codec_ctx;
+       }
+
+       /*
+        * Invoke type-specific decoder.
+        */
+       return type_descriptor->ber_decoder(opt_codec_ctx, type_descriptor,
+               struct_ptr,     /* Pointer to the destination structure */
+               ptr, size,      /* Buffer and its size */
+               0               /* Default tag mode is 0 */
+               );
+}
+
+/*
+ * Check the set of <TL<TL<TL...>>> tags matches the definition.
+ */
+asn_dec_rval_t
+ber_check_tags(asn_codec_ctx_t *opt_codec_ctx,
+               asn_TYPE_descriptor_t *td, asn_struct_ctx_t *opt_ctx,
+               const void *ptr, size_t size, int tag_mode, int last_tag_form,
+               ber_tlv_len_t *last_length, int *opt_tlv_form) {
+       ssize_t consumed_myself = 0;
+       ssize_t tag_len;
+       ssize_t len_len;
+       ber_tlv_tag_t tlv_tag;
+       ber_tlv_len_t tlv_len;
+       ber_tlv_len_t limit_len = -1;
+       int expect_00_terminators = 0;
+       int tlv_constr = -1;    /* If CHOICE, opt_tlv_form is not given */
+       int step = opt_ctx ? opt_ctx->step : 0; /* Where we left previously */
+       int tagno;
+
+       /*
+        * Make sure we didn't exceed the maximum stack size.
+        */
+       if(_ASN_STACK_OVERFLOW_CHECK(opt_codec_ctx))
+               RETURN(RC_FAIL);
+
+       /*
+        * So what does all this implicit skip stuff mean?
+        * Imagine two types,
+        *      A ::= [5] IMPLICIT      T
+        *      B ::= [2] EXPLICIT      T
+        * Where T is defined as
+        *      T ::= [4] IMPLICIT SEQUENCE { ... }
+        * 
+        * Let's say, we are starting to decode type A, given the
+        * following TLV stream: <5> <0>. What does this mean?
+        * It means that the type A contains type T which is,
+        * in turn, empty.
+        * Remember though, that we are still in A. We cannot
+        * just pass control to the type T decoder. Why? Because
+        * the type T decoder expects <4> <0>, not <5> <0>.
+        * So, we must make sure we are going to receive <5> while
+        * still in A, then pass control to the T decoder, indicating
+        * that the tag <4> was implicitly skipped. The decoder of T
+        * hence will be prepared to treat <4> as valid tag, and decode
+        * it appropriately.
+        */
+
+       tagno = step    /* Continuing where left previously */
+               + (tag_mode==1?-1:0)
+               ;
+       ASN_DEBUG("ber_check_tags(%s, size=%ld, tm=%d, step=%d, tagno=%d)",
+               td->name, (long)size, tag_mode, step, tagno);
+       /* assert(td->tags_count >= 1) May not be the case for CHOICE or ANY */
+
+       if(tag_mode == 0 && tagno == td->tags_count) {
+               /*
+                * This must be the _untagged_ ANY type,
+                * which outermost tag isn't known in advance.
+                * Fetch the tag and length separately.
+                */
+               tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
+               switch(tag_len) {
+               case -1: RETURN(RC_FAIL);
+               case 0: RETURN(RC_WMORE);
+               }
+               tlv_constr = BER_TLV_CONSTRUCTED(ptr);
+               len_len = ber_fetch_length(tlv_constr,
+                       (const char *)ptr + tag_len, size - tag_len, &tlv_len);
+               switch(len_len) {
+               case -1: RETURN(RC_FAIL);
+               case 0: RETURN(RC_WMORE);
+               }
+               ASN_DEBUG("Advancing %ld in ANY case",
+                       (long)(tag_len + len_len));
+               ADVANCE(tag_len + len_len);
+       } else {
+               assert(tagno < td->tags_count); /* At least one loop */
+       }
+       for((void)tagno; tagno < td->tags_count; tagno++, step++) {
+
+               /*
+                * Fetch and process T from TLV.
+                */
+               tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
+                       ASN_DEBUG("Fetching tag from {%p,%ld}: "
+                               "len %ld, step %d, tagno %d got %s",
+                               ptr, (long)size,
+                               (long)tag_len, step, tagno,
+                               ber_tlv_tag_string(tlv_tag));
+               switch(tag_len) {
+               case -1: RETURN(RC_FAIL);
+               case 0: RETURN(RC_WMORE);
+               }
+
+               tlv_constr = BER_TLV_CONSTRUCTED(ptr);
+
+               /*
+                * If {I}, don't check anything.
+                * If {I,B,C}, check B and C unless we're at I.
+                */
+               if(tag_mode != 0 && step == 0) {
+                       /*
+                        * We don't expect tag to match here.
+                        * It's just because we don't know how the tag
+                        * is supposed to look like.
+                        */
+               } else {
+                   assert(tagno >= 0); /* Guaranteed by the code above */
+                   if(tlv_tag != td->tags[tagno]) {
+                       /*
+                        * Unexpected tag. Too bad.
+                        */
+                       ASN_DEBUG("Expected: %s, "
+                               "expectation failed (tn=%d, tm=%d)",
+                               ber_tlv_tag_string(td->tags[tagno]),
+                               tagno, tag_mode
+                       );
+                       RETURN(RC_FAIL);
+                   }
+               }
+
+               /*
+                * Attention: if there are more tags expected,
+                * ensure that the current tag is presented
+                * in constructed form (it contains other tags!).
+                * If this one is the last one, check that the tag form
+                * matches the one given in descriptor.
+                */
+               if(tagno < (td->tags_count - 1)) {
+                       if(tlv_constr == 0) {
+                               ASN_DEBUG("tlv_constr = %d, expfail",
+                                       tlv_constr);
+                               RETURN(RC_FAIL);
+                       }
+               } else {
+                       if(last_tag_form != tlv_constr
+                       && last_tag_form != -1) {
+                               ASN_DEBUG("last_tag_form %d != %d",
+                                       last_tag_form, tlv_constr);
+                               RETURN(RC_FAIL);
+                       }
+               }
+
+               /*
+                * Fetch and process L from TLV.
+                */
+               len_len = ber_fetch_length(tlv_constr,
+                       (const char *)ptr + tag_len, size - tag_len, &tlv_len);
+               ASN_DEBUG("Fetchinig len = %ld", (long)len_len);
+               switch(len_len) {
+               case -1: RETURN(RC_FAIL);
+               case 0: RETURN(RC_WMORE);
+               }
+
+               /*
+                * FIXME
+                * As of today, the chain of tags
+                * must either contain several indefinite length TLVs,
+                * or several definite length ones.
+                * No mixing is allowed.
+                */
+               if(tlv_len == -1) {
+                       /*
+                        * Indefinite length.
+                        */
+                       if(limit_len == -1) {
+                               expect_00_terminators++;
+                       } else {
+                               ASN_DEBUG("Unexpected indefinite length "
+                                       "in a chain of definite lengths");
+                               RETURN(RC_FAIL);
+                       }
+                       ADVANCE(tag_len + len_len);
+                       continue;
+               } else {
+                       if(expect_00_terminators) {
+                               ASN_DEBUG("Unexpected definite length "
+                                       "in a chain of indefinite lengths");
+                               RETURN(RC_FAIL);
+                       }
+               }
+
+               /*
+                * Check that multiple TLVs specify ever decreasing length,
+                * which is consistent.
+                */
+               if(limit_len == -1) {
+                       limit_len    = tlv_len + tag_len + len_len;
+                       if(limit_len < 0) {
+                               /* Too great tlv_len value? */
+                               RETURN(RC_FAIL);
+                       }
+               } else if(limit_len != tlv_len + tag_len + len_len) {
+                       /*
+                        * Inner TLV specifies length which is inconsistent
+                        * with the outer TLV's length value.
+                        */
+                       ASN_DEBUG("Outer TLV is %ld and inner is %ld",
+                               (long)limit_len, (long)tlv_len);
+                       RETURN(RC_FAIL);
+               }
+
+               ADVANCE(tag_len + len_len);
+
+               limit_len -= (tag_len + len_len);
+               if((ssize_t)size > limit_len) {
+                       /*
+                        * Make sure that we won't consume more bytes
+                        * from the parent frame than the inferred limit.
+                        */
+                       size = limit_len;
+               }
+       }
+
+       if(opt_tlv_form)
+               *opt_tlv_form = tlv_constr;
+       if(expect_00_terminators)
+               *last_length = -expect_00_terminators;
+       else
+               *last_length = tlv_len;
+
+       RETURN(RC_OK);
+}