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Re: [Qemu-devel] [PATCH v2] make check-unit: use after free in test-opts
From: |
Andrey Shinkevich |
Subject: |
Re: [Qemu-devel] [PATCH v2] make check-unit: use after free in test-opts-visitor |
Date: |
Mon, 5 Aug 2019 15:09:30 +0000 |
On 02/08/2019 14:34, Markus Armbruster wrote:
> Andrey Shinkevich <address@hidden> writes:
>
>> In struct OptsVisitor, repeated_opts member points to a list in the
>> unprocessed_opts hash table after the list has been destroyed. A
>> subsequent call to visit_type_int() references the deleted list. It
>> results in use-after-free issue.
>
> Let's mention the reproducer: valgrind tests/test/opts-visitor.
>
>> Also, the Visitor object call back
>> functions are supposed to set the Error parameter in case of failure.
>
> As far as I can tell, they all do. The only place where you set an
> error is the new failure you add to lookup_scalar().
>
The story behind the comment is that the original
tests/test-opts-visitor fails being run under the Valgrind with the
error message:
test-opts-visitor: util/error.c:276: error_free_or_abort: Assertion
`errp && *errp' failed.
coming from
assert(errp && *errp);
error_free_or_abort (util/error.c:276)
test_opts_range_beyond (tests/test-opts-visitor.c:241)
because g_queue_peek_head() returns NULL under the Valgrind and errp
stays unset.
Without the Valgrind, the g_queue_peek_head() returns a non-zero pointer
and the opts_type_int64() sets the following error:
"Parameter '\340F\212\274\267U' expects an int64 value or range",
err_class = ERROR_CLASS_GENERIC_ERROR, src = 0x55b7bbc02163
"qapi/opts-visitor.c",
func = 0x55b7bbc02410 <__func__.14916> "opts_type_int64", line = 433,
hint = 0x0}
so, error_free_or_abort() doesn't abort and the test case passes.
I will remove the comment in v3.
Andrey
>> A new mode ListMode::LM_TRAVERSED is declared to mark the list
>> traversal completed.
>>
>> Suggested-by: Markus Armbruster <address@hidden>
>> Signed-off-by: Andrey Shinkevich <address@hidden>
>> ---
>>
>> v2:
>> 01: A new mode LM_TRAVERSED has been introduced to check instead of the
>> repeated_opts pointer for NULL.
>>
>> qapi/opts-visitor.c | 78
>> +++++++++++++++++++++++++++++++++--------------------
>> 1 file changed, 49 insertions(+), 29 deletions(-)
>>
>> diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c
>> index 324b197..23ac383 100644
>> --- a/qapi/opts-visitor.c
>> +++ b/qapi/opts-visitor.c
>> @@ -22,33 +22,42 @@
>>
>> enum ListMode
>> {
>> - LM_NONE, /* not traversing a list of repeated options */
>> -
>> - LM_IN_PROGRESS, /* opts_next_list() ready to be called.
>> - *
>> - * Generating the next list link will consume the
>> most
>> - * recently parsed QemuOpt instance of the repeated
>> - * option.
>> - *
>> - * Parsing a value into the list link will examine
>> the
>> - * next QemuOpt instance of the repeated option,
>> and
>> - * possibly enter LM_SIGNED_INTERVAL or
>> - * LM_UNSIGNED_INTERVAL.
>> - */
>> -
>> - LM_SIGNED_INTERVAL, /* opts_next_list() has been called.
>> - *
>> - * Generating the next list link will consume the
>> most
>> - * recently stored element from the signed
>> interval,
>> - * parsed from the most recent QemuOpt instance of
>> the
>> - * repeated option. This may consume QemuOpt itself
>> - * and return to LM_IN_PROGRESS.
>> - *
>> - * Parsing a value into the list link will store
>> the
>> - * next element of the signed interval.
>> - */
>> -
>> - LM_UNSIGNED_INTERVAL /* Same as above, only for an unsigned interval. */
>> + LM_NONE, /* not traversing a list of repeated options */
>> +
>> + LM_IN_PROGRESS, /*
>> + * opts_next_list() ready to be called.
>> + *
>> + * Generating the next list link will consume the
>> most
>> + * recently parsed QemuOpt instance of the
>> repeated
>> + * option.
>> + *
>> + * Parsing a value into the list link will
>> examine the
>> + * next QemuOpt instance of the repeated option,
>> and
>> + * possibly enter LM_SIGNED_INTERVAL or
>> + * LM_UNSIGNED_INTERVAL.
>> + */
>> +
>> + LM_SIGNED_INTERVAL, /*
>> + * opts_next_list() has been called.
>> + *
>> + * Generating the next list link will consume the
>> most
>> + * recently stored element from the signed
>> interval,
>> + * parsed from the most recent QemuOpt instance
>> of the
>> + * repeated option. This may consume QemuOpt
>> itself
>> + * and return to LM_IN_PROGRESS.
>> + *
>> + * Parsing a value into the list link will store
>> the
>> + * next element of the signed interval.
>> + */
>> +
>> + LM_UNSIGNED_INTERVAL, /* Same as above, only for an unsigned interval.
>> */
>> +
>> + LM_TRAVERSED /*
>> + * opts_next_list() has been called.
>> + *
>> + * No more QemuOpt instance in the list.
>> + * The traversal has been completed.
>> + */
>> };
>>
>> typedef enum ListMode ListMode;
>
> Please don't change the spacing without need. The hunk should look like
> this:
>
> @@ -24,7 +24,8 @@ enum ListMode
> {
> LM_NONE, /* not traversing a list of repeated options */
>
> - LM_IN_PROGRESS, /* opts_next_list() ready to be called.
> + LM_IN_PROGRESS, /*
> + * opts_next_list() ready to be called.
> *
> * Generating the next list link will consume
> the most
> * recently parsed QemuOpt instance of the
> repeated
> @@ -36,7 +37,8 @@ enum ListMode
> * LM_UNSIGNED_INTERVAL.
> */
>
> - LM_SIGNED_INTERVAL, /* opts_next_list() has been called.
> + LM_SIGNED_INTERVAL, /*
> + * opts_next_list() has been called.
> *
> * Generating the next list link will consume
> the most
> * recently stored element from the signed
> interval,
> @@ -48,7 +50,14 @@ enum ListMode
> * next element of the signed interval.
> */
>
> - LM_UNSIGNED_INTERVAL /* Same as above, only for an unsigned interval.
> */
> + LM_UNSIGNED_INTERVAL, /* Same as above, only for an unsigned
> interval. */
> +
> + LM_TRAVERSED /*
> + * opts_next_list() has been called.
> + *
> + * No more QemuOpt instance in the list.
> + * The traversal has been completed.
> + */
> };
>
> typedef enum ListMode ListMode;
>
>> @@ -238,6 +247,8 @@ opts_next_list(Visitor *v, GenericList *tail, size_t
>> size)
>> OptsVisitor *ov = to_ov(v);
>>
>> switch (ov->list_mode) {
>> + case LM_TRAVERSED:
>> + return NULL;
>> case LM_SIGNED_INTERVAL:
>> case LM_UNSIGNED_INTERVAL:
>> if (ov->list_mode == LM_SIGNED_INTERVAL) {
>> @@ -258,6 +269,8 @@ opts_next_list(Visitor *v, GenericList *tail, size_t
>> size)
>> opt = g_queue_pop_head(ov->repeated_opts);
>> if (g_queue_is_empty(ov->repeated_opts)) {
>> g_hash_table_remove(ov->unprocessed_opts, opt->name);
>> + ov->repeated_opts = NULL;
>> + ov->list_mode = LM_TRAVERSED;
>> return NULL;
>> }
>> break;
>> @@ -289,8 +302,11 @@ opts_end_list(Visitor *v, void **obj)
>>
>> assert(ov->list_mode == LM_IN_PROGRESS ||
>> ov->list_mode == LM_SIGNED_INTERVAL ||
>> - ov->list_mode == LM_UNSIGNED_INTERVAL);
>> - ov->repeated_opts = NULL;
>> + ov->list_mode == LM_UNSIGNED_INTERVAL ||
>> + ov->list_mode == LM_TRAVERSED);
>> + if (ov->list_mode != LM_TRAVERSED) {
>> + ov->repeated_opts = NULL;
>> + }
>
> What's wrong with zapping ov->repeated_opts unconditionally?
>
>> ov->list_mode = LM_NONE;
>> }
>>
>> @@ -306,6 +322,10 @@ lookup_scalar(const OptsVisitor *ov, const char *name,
>> Error **errp)
>> list = lookup_distinct(ov, name, errp);
>> return list ? g_queue_peek_tail(list) : NULL;
>> }
>> + if (ov->list_mode == LM_TRAVERSED) {
>> + error_setg(errp, QERR_INVALID_PARAMETER, name);
>
> Beware, @name is null when visiting list members. The test still passes
> for me, since g_strdup_vprintf() formats a null argument to %s as
> "(null)".
>
> For what it's worth, the qobject input visitor uses
> QERR_MISSING_PARAMETER with a made-up name. Computing the name is
> pretty elaborate, see full_name_nth(). I'd rather not duplicate that
> here.
>
> Suggest something like
>
> error_setg(errp, "Fewer list elements than expected");
>
> The error message fails to mention the name of the list. Bad, but the
> error is a corner case; we don't normally visit beyond the end of the
> list. For a better message, we'd have to have start_list() store its
> @name in struct OptsVisitor. I'm not asking you to do that now.
>
Will I do that work to add the @name of the list to the struct
OptsVisitor in a following series?
>> + return NULL;
>> + }
>> assert(ov->list_mode == LM_IN_PROGRESS);
>> return g_queue_peek_head(ov->repeated_opts);
>> }
>
> I checked the remaining uses of ->list_mode, and I think they are okay.
>
Thank you. I also had not noticed any potential issue with the list_mode.
Andrey
--
With the best regards,
Andrey Shinkevich