CBOR-to-JSON: fix memory leak when parsing invalid CBOR

[niooss-ledger]

When function text_string_to_escaped successfully parses a string and fails to parse the next value (cbor_value_finish_string_iteration returns an error), it correctly propagates the error but the string is never freed.

This can be reproduced with:

make CC='clang -g -fsanitize=address'
printf '\x82\x60\xff' | ./bin/cbordump -j

clang's Address Sanitizer reports:

=================================================================
==20317==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 1 byte(s) in 1 object(s) allocated from:
    #0 0x560b654b9916 in __interceptor_realloc (/tinycbor/bin/cbordump+0xa4916) (BuildId: f9933666b5d987b21f68c2887de4aebe93bc2bef)
    #1 0x560b654f5c18 in escape_text_string /tinycbor/src/cbortojson.c:331:15
    #2 0x560b654f3e29 in text_string_to_escaped /tinycbor/src/cbortojson.c:377:19
    #3 0x560b654f267d in value_to_json /tinycbor/src/cbortojson.c:674:19
    #4 0x560b654f34c2 in array_to_json /tinycbor/src/cbortojson.c:545:25
    #5 0x560b654f2085 in value_to_json /tinycbor/src/cbortojson.c:627:19
    #6 0x560b654f1baf in cbor_value_to_json_advance /tinycbor/src/cbortojson.c:816:12
    #7 0x560b654ea928 in dumpFile /tinycbor/tools/cbordump/cbordump.c:76:19
    #8 0x560b654ead2b in main /tinycbor/tools/cbordump/cbordump.c:149:9
    #9 0x7fa9d7629d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16

SUMMARY: AddressSanitizer: 1 byte(s) leaked in 1 allocation(s).

Fix this by freeing the string when cbor_value_finish_string_iteration fails.

Fixes: e072bc1 ("CBOR-to-JSON: do properly escape JSON strings", #274)

[thiagomacieira]

I'll add a Mac -fsanitize=address build to my local branch to see if this is caught by the existing tests.

[thiagomacieira]

I'll add a Mac -fsanitize=address build to my local branch to see if this is caught by the existing tests.

No failures reported in https://github.com/thiagomacieira/tinycbor/actions/runs/13861024310/job/38789295761.

We don't test ToJson with invalid content. Something for the future, I guess...