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Fix memory errors when trim causes testcase growth (#881) (#903)

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* Revert "fixed potential double free in custom trim (#881)"

This reverts commit e9d2f72382.

* Revert "fix custom trim for increasing data"

This reverts commit 86a8ef168d.

* Fix memory errors when trim causes testcase growth

Modify trim_case_custom to avoid writing into in_buf because
some custom mutators can cause the testcase to grow rather than
shrink.

Instead of modifying in_buf directly, we write the update out
to the disk when trimming is complete, and then the caller is
responsible for refreshing the in-memory buffer from the file.

This is still a bit sketchy because it does need to modify q->len in
order to notify the upper layers that something changed, and it could
end up telling upper layer code that the q->len is *bigger* than
the buffer (q->testcase_buf) that contains it, which is asking
for trouble down the line somewhere...

* Fix an unlikely situation

Put back some `unlikely()` calls that were in
the e9d2f72382 commit that was
reverted.
This commit is contained in:
realmadsci
2021-05-06 18:14:16 -04:00
committed by GitHub
parent 187ca8e18b
commit 1d9a3d955c
4 changed files with 38 additions and 45 deletions
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67
src/afl-fuzz-mutators.c
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@ -305,16 +305,14 @@ struct custom_mutator *load_custom_mutator(afl_state_t *afl, const char *fn) {
}
// Custom testcase trimming.
u8 trim_case_custom(afl_state_t *afl, struct queue_entry *q, u8 **in_buf_p,
u8 trim_case_custom(afl_state_t *afl, struct queue_entry *q, u8 *in_buf,
struct custom_mutator *mutator) {
// We need to pass pointers around, as growing testcases may need to realloc.
u8 *in_buf = *in_buf_p;
u8 needs_write = 0, fault = 0;
u8 fault = 0;
u32 trim_exec = 0;
u32 orig_len = q->len;
u32 out_len = 0;
u8* out_buf = NULL;
u8 val_buf[STRINGIFY_VAL_SIZE_MAX];
@ -401,40 +399,33 @@ u8 trim_case_custom(afl_state_t *afl, struct queue_entry *q, u8 **in_buf_p,
if (likely(retlen && cksum == q->exec_cksum)) {
// Check if we got a new retbuf and to memcpy our buf.
if (in_buf != retbuf) {
if (afl_realloc((void **)in_buf_p, retlen) == NULL) {
FATAL("can not allocate memory for trim");
}
in_buf = *in_buf_p;
memcpy(in_buf, retbuf, retlen);
q->len = retlen;
}
/* Let's save a clean trace, which will be needed by
update_bitmap_score once we're done with the trimming stuff. */
update_bitmap_score once we're done with the trimming stuff.
Use out_buf NULL check to make this only happen once per trim. */
if (!needs_write) {
if (!out_buf) {
needs_write = 1;
memcpy(afl->clean_trace_custom, afl->fsrv.trace_bits,
afl->fsrv.map_size);
}
if (afl_realloc((void **)&out_buf, retlen) == NULL) {
FATAL("can not allocate memory for trim");
}
out_len = retlen;
memcpy(out_buf, retbuf, retlen);
/* Tell the custom mutator that the trimming was successful */
afl->stage_cur = mutator->afl_custom_post_trim(mutator->data, 1);
if (afl->not_on_tty && afl->debug) {
SAYF("[Custom Trimming] SUCCESS: %u/%u iterations (now at %u bytes)",
afl->stage_cur, afl->stage_max, q->len);
afl->stage_cur, afl->stage_max, out_len);
}
@ -467,16 +458,10 @@ u8 trim_case_custom(afl_state_t *afl, struct queue_entry *q, u8 **in_buf_p,
}
if (afl->not_on_tty && afl->debug) {
SAYF("[Custom Trimming] DONE: %u bytes -> %u bytes", orig_len, q->len);
}
/* If we have made changes to in_buf, we also need to update the on-disk
/* If we have made changes, we also need to update the on-disk
version of the test case. */
if (needs_write) {
if (out_buf) {
s32 fd;
@ -486,16 +471,28 @@ u8 trim_case_custom(afl_state_t *afl, struct queue_entry *q, u8 **in_buf_p,
if (fd < 0) { PFATAL("Unable to create '%s'", q->fname); }
ck_write(fd, in_buf, q->len, q->fname);
ck_write(fd, out_buf, out_len, q->fname);
close(fd);
/* Update the queue's knowledge of length as soon as we write the file.
We do this here so that exit/error cases that *don't* update the file also
don't update q->len. */
q->len = out_len;
memcpy(afl->fsrv.trace_bits, afl->clean_trace_custom, afl->fsrv.map_size);
update_bitmap_score(afl, q);
}
if (afl->not_on_tty && afl->debug) {
SAYF("[Custom Trimming] DONE: %u bytes -> %u bytes", orig_len, q->len);
}
abort_trimming:
if (out_buf) afl_free(out_buf);
afl->bytes_trim_out += q->len;
return fault;