[PATCH][libbacktrace] Fix segfault upon allocation failure

[Tom de Vries]

Hi,

If the allocation of abbrevs->abbrevs in read_abbrevs fails, then
abbrevs->num_abbrevs remains nonzero, and consequently free_abbrevs will
segfault when accessing abbrevs->abbrevs.

Fix this by setting abbrevs->num_abbrevs only after abbrevs->abbrevs
allocation has succeeded.

Bootstrapped and reg-tested on x86_64.

OK for trunk?

Thanks,
- Tom

[libbacktrace] Fix segfault upon allocation failure

2018-11-27  Tom de Vries  <tdevr...@suse.de>

        * dwarf.c (read_abbrevs): Fix handling of abbrevs->abbrevs allocation
        failure.

---
 libbacktrace/dwarf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libbacktrace/dwarf.c b/libbacktrace/dwarf.c
index 4e93f120820..34543747c8f 100644
--- a/libbacktrace/dwarf.c
+++ b/libbacktrace/dwarf.c
@@ -1105,13 +1105,13 @@ read_abbrevs (struct backtrace_state *state, uint64_t 
abbrev_offset,
   if (num_abbrevs == 0)
     return 1;
 
-  abbrevs->num_abbrevs = num_abbrevs;
   abbrevs->abbrevs = ((struct abbrev *)
                      backtrace_alloc (state,
                                       num_abbrevs * sizeof (struct abbrev),
                                       error_callback, data));
   if (abbrevs->abbrevs == NULL)
     return 0;
+  abbrevs->num_abbrevs = num_abbrevs;
   memset (abbrevs->abbrevs, 0, num_abbrevs * sizeof (struct abbrev));
 
   num_abbrevs = 0;