libctf: make ctf_dump not crash on OOM

ctf_dump calls ctf_str_append extensively but never checks to see if it
returns NULL (on OOM).  If it ever does, we truncate the string we are
appending to and leak it!

Instead, create a variant of ctf_str_append that returns the *original
string* on OOM, and use it in ctf-dump.  It is far better to omit a tiny
piece of a dump on OOM than to omit a bigger piece, and it is also
better to do this in what is after all purely debugging code than it is
to uglify ctf-dump.c with huge numbers of checks for the out-of-memory
case.  Slightly truncated debugging output is better than no debugging
output at all and an out-of-memory message.

New in v4.

libctf/
	* ctf-impl.h (ctf_str_append_noerr): Declare.
	* ctf-util.c (ctf_str_append_noerr): Define in terms of
	ctf_str_append.
	* ctf-dump.c (str_append): New, call it.
	(ctf_dump_format_type): Use str_append, not ctf_str_append.
	(ctf_dump_label): Likewise.
	(ctf_dump_objts): Likewise.
	(ctf_dump_funcs): Likewise.
	(ctf_dump_var): Likewise.
	(ctf_dump_member): Likewise.
	(ctf_dump_type): Likewise.
	(ctf_dump): Likewise.

1 files changed, 14 insertions, 1 deletions

diff --git a/libctf/ctf-util.c b/libctf/ctf-util.c
index d10b2b5..d4a1c5a 100644
--- a/libctf/ctf-util.c
+++ b/libctf/ctf-util.c
@@ -103,7 +103,7 @@ ctf_sym_to_elf64 (const Elf32_Sym *src, Elf64_Sym *dst)
   return dst;
 }
 
-/* A string appender working on dynamic strings.  */
+/* A string appender working on dynamic strings.  Returns NULL on OOM.  */
 
 char *
 ctf_str_append (char *s, const char *append)
@@ -127,6 +127,19 @@ ctf_str_append (char *s, const char *append)
   return s;
 }
 
+/* A version of ctf_str_append that returns the old string on OOM.  */
+
+char *
+ctf_str_append_noerr (char *s, const char *append)
+{
+  char *new_s;
+
+  new_s = ctf_str_append (s, append);
+  if (!new_s)
+    return s;
+  return new_s;
+}
+
 /* A realloc() that fails noisily if called with any ctf_str_num_users.  */
 void *
 ctf_realloc (ctf_file_t *fp, void *ptr, size_t size)