Re: [libvirt] [PATCH] test: fix segfault in networkxml2argvtest

This bug resolves https://bugzilla.redhat.com/show_bug.cgi?id=810100 rpm builds for i686 were failing with a segfault in networkxml2argvtest. Running under valgrind showed that a region of memory was being referenced after it had been freed (as the result of realloc - see the valgrind report in the BZ). The problem (in replaceTokens() - added in commit 22ec60, meaning this bug was in 0.9.10 and 0.9.11) was that the pointers token_start and token_end were being computed based on the value of *buf, then *buf was being realloc'ed (potentially moving it), then token_start and token_end were used without recomputing them to account for movement of *buf. The solution is to change the code so that token_start and token_end are offsets into *buf rather than pointers. This way there is only a single pointer to the buffer, and nothing needs readjusting after a realloc. (You may note that some uses of token_start/token_end didn't need to be changed to add in "*buf +" - that's because there ended up being a +*buf and -*buf which canceled each other out). DV gets the credit for finding this bug and pointing out the valgrind report. --- tests/networkxml2argvtest.c | 13 +++++++------ 1 files changed, 7 insertions(+), 6 deletions(-) diff --git a/tests/networkxml2argvtest.c b/tests/networkxml2argvtest.c index cf00181..87519e4 100644 --- a/tests/networkxml2argvtest.c +++ b/tests/networkxml2argvtest.c @@ -18,18 +18,19 @@ /* Replace all occurrences of @token in @buf by @replacement and adjust size of * @buf accordingly. Returns 0 on success and -1 on out-of-memory errors. */ static int replaceTokens(char **buf, const char *token, const char *replacement) { - char *token_start, *token_end; + size_t token_start, token_end; size_t buf_len, rest_len; const size_t token_len = strlen(token); const size_t replacement_len = strlen(replacement); const int diff = replacement_len - token_len; buf_len = rest_len = strlen(*buf) + 1; - token_end = *buf; + token_end = 0; for (;;) { - token_start = strstr(token_end, token); - if (token_start == NULL) + char *match = strstr(*buf + token_end, token); + if (match == NULL) break; + token_start = match - *buf; rest_len -= token_start + token_len - token_end; token_end = token_start + token_len; buf_len += diff; @@ -37,8 +38,8 @@ static int replaceTokens(char **buf, const char *token, const char *replacement) if (VIR_REALLOC_N(*buf, buf_len)< 0) return -1; if (diff != 0) - memmove(token_end + diff, token_end, rest_len); - memcpy(token_start, replacement, replacement_len); + memmove(*buf + token_end + diff, *buf + token_end, rest_len); + memcpy(*buf + token_start, replacement, replacement_len); token_end += diff; } /* if diff< 0, we could shrink the buffer here... */