RFR: 8220095: Assertion failure when symlink (with different name) is used for lib/modules file
Ioi Lam
ioi.lam at oracle.com
Wed Mar 13 00:14:28 UTC 2019
On 3/12/19 4:42 PM, Jiangli Zhou wrote:
> One of my early experimental revision actually simply used strcmp to
> compare the full path and to also recorded the full path for the
> canonical modules name.
>
> I decide to not go with that because there is no guarantee that the
> path given to is_modules_image check is in canonical form and it
> diverts from the existing assumptions about the usages of this API
> (checking the file name only).
If someone is calling is_modules_image() with an non-canonical file
name, is there a guarantee that they will keep the file name part unchanged?
Comparing the filename only is just wrong. I don't think we can do that
in any fix for this bug.
Thanks
- Ioi
> The "/dev/fd/0" example you have is not a direct result of the current
> fix but is an inherent issue of the modules check. Any file with the
> same designated modules name would pass the check. If we want to
> safely use the full path comparison, we need to closely exam all the
> call sites and make sure all the places use canonical paths. I'll some
> analysis on that.
>
> Thanks,
> Jiangli
>
> On Tue, Mar 12, 2019 at 4:13 PM Ioi Lam <ioi.lam at oracle.com
> <mailto:ioi.lam at oracle.com>> wrote:
>
> This seems more complicated that it needs to be.
>
> + The VM can have at most one modules file.
>
> + The only reason the VM calls is_modules_image(p) is to check
> whether p, a full path, is THE modules file. In all cases, p is
> actually derived from the singleton ClassPathImageEntry::name().
> It's just that in some cases, such as in the logging code, we have
> lost the pointer to the ClassPathImageEntry, and just have the
> full path.
>
> + On line 722 of
> http://cr.openjdk.java.net/~jiangli/8220095/webrev.01/src/hotspot/share/classfile/classLoader.cpp.sdiff.html,
> you already have a full path of THE modules file.
>
> Why can't you just do a strcmp of the full path? That's much
> simpler, and more importantly, correct. Your version will return
> true for "/dev/fd/0" for the test case described in the bug
> report. That doesn't seem to be correct.
>
>
> Thanks
> - Ioi
>
>
>
> On 3/12/19 9:10 AM, Jiangli Zhou wrote:
>> Hi Ioi,
>>
>> Thanks for looking into this also.
>>
>> On Mon, Mar 11, 2019 at 8:19 PM Ioi Lam <ioi.lam at oracle.com
>> <mailto:ioi.lam at oracle.com>> wrote:
>>
>>
>>
>> On 3/11/19 7:30 PM, Ioi Lam wrote:
>> > I think this patch should be further improved.
>> >
>> > First of all, the original code is problematic:
>> >
>> > static bool is_modules_image(const char* name) { return
>> > string_ends_with(name, MODULES_IMAGE_NAME); }
>> >
>> > So if we have a file called /foo/bar/xxxmodules, this
>> function returns
>> > true!
>> >
>>
>> BTW, If you have a symlink JAVA_HOME/lib/modules ->
>> JAVA_HOME/lib/r,
>> then your new version of is_modules_image will return true
>> for any jar
>> file.
>>
>> See
>> http://hg.openjdk.java.net/jdk/jdk/file/f984aca565c1/src/hotspot/share/oops/instanceKlass.cpp#l3370
>>
>> if (ClassLoader::is_modules_image(cfs->source())) {
>> info_stream.print(" source: jrt:/%s", module_name);
>> }
>>
>> This will cause all classes loaded from modular JAR files be
>> incorrectly
>> printed as "jrt://"
>>
>> Even if you also use the last "/" path separator, it's still
>> not safe to
>> use the filename alone to determine whether a file is indeed
>> the modules
>> image file. I.e., what if you have JAVA_HOME/lib/modules ->
>> JAVA_HOME/lib/test.jar?
>>
>>
>> The current bug addresses the practical issue when the modules is
>> a sym link to a unique content identifier. Using modules as a
>> link to any arbitrary file is not addressed by this bug. It's in
>> the same area but a different issue.
>>
>> If lib/modules ->lib/test.jar, or lib/modules -> ../ (or any
>> other arbitrary file/dir) is done, the VM fails differently. This
>> is the same as if you replace libjvm.so with another random file.
>>
>> The canonical modules name is obtained from the actual modules
>> image during setup_boot_search_path, so it's guaranteed to refer
>> to the correct identifier. Checking the file name after '/' is safe.
>>
>> The substring issue that you pointed out has not been observed,
>> as that's prevented by the naming method of the content
>> identifiers. The substring issue however can be solved relatively
>> inexpensively by making sure the check covers the entire file
>> name after '/'.
>>
>>
>>
>> Also, I think we can have a version that's simpler than what
>> I proposed
>> below:
>>
>> + We can have at most a single ClassPathImageEntry.
>> + All calls to ClassLoader::is_modules_image() are made
>> after the
>> ClassPathImageEntry is created
>>
>> so:
>>
>> static bool is_modules_image(const char* name) {
>> if (ClassPathImageEntry::singleton() != NULL) {
>> return strcmp(name,
>> ClassPathImageEntry::singleton()->name()) == 0);
>> } else {
>> assert(_exploded_entries != NULL, "must be running
>> with exploded
>> modules");
>> return false;
>> }
>> }
>>
>>
>> The argument passed can be a path to the modules, so strcmp
>> cannot be simply used for 'name'.
>>
>> static bool is_modules_image(const char* name) {
>>
>> if (Arguments::has_jimage()) {
>>
>> assert(_modules_image_name != NULL, "must be set");
>>
>> const char* p = skip_directories(name);
>>
>> return strcmp(p, _modules_image_name) == 0;
>>
>> }
>>
>> return false;
>>
>> }
>>
>>
>> I've revised the is_modules_image() to also cover the substring
>> issue.
>>
>>
>>
>>
>>
>> This function should be changed to always return true
>>
>> bool ClassPathImageEntry::is_modules_image() const {
>> - return ClassLoader::is_modules_image(name());
>> + return true;
>> }
>>
>>
>> Leaving ClassPathImageEntry::is_modules_image() without changing
>> is safer, so it can make sure the ClassPathImageEntry name agrees
>> with the canonical modules name.
>>
>>
>>
>> To make sure we don't call is_modules_image before
>> ClassPathImageEntry
>> is created, we could do
>>
>> static bool is_modules_image(const char* name) {
>> DEBUG_ONLY(_is_modules_image_called = true;)
>> ...
>> }
>>
>>
>> The 'assert(_modules_image_name != NULL, "must be set")' check
>> makes sure is_modules_image(const char*) is not called
>> before setup_boot_search_path. There is no need to add additional
>> flag.
>>
>> Thanks,
>> Jiangli
>>
>>
>>
>> ClassPathImageEntry::ClassPathImageEntry() {
>> assert(_singleton == NULL, "...");
>> assert(!_is_modules_image_called, "Don't call
>> ClassLoader::is_modules_image() before ClassPathImageEntry is
>> allocated");
>> ...
>>
>>
>> Thanks
>> - Ioi
>>
>>
>> > It seems the patch simply makes the code more convoluted.
>> Instead,
>> > shouldn't we just open the file and check the magic number?
>> >
>> > If performance is important, we can use a cache, because we
>> allow a
>> > single module image:
>> >
>> > static bool is_modules_image(const char* name) {
>> > static const char* singleton_module_name = NULL;
>> >
>> > if (singleton_module_name != NULL) {
>> > return strcmp(name, singleton_module_name) == 0;
>> > }
>> > // open <name> and check magic number
>> > if (good) {
>> > singleton_module_name = os::strdup(name);
>> > return true;
>> > }
>> > return false;
>> > }
>> >
>> > Thanks
>> > - Ioi
>> >
>> > On 3/11/19 10:51 AM, Jiangli Zhou wrote:
>> >> On Mon, Mar 11, 2019 at 8:44 AM Calvin Cheung
>> <calvin.cheung at oracle.com <mailto:calvin.cheung at oracle.com>>
>> >> wrote:
>> >>
>> >>> Hi Jiangli,
>> >>>
>> >>> The updated webrev looks good.
>> >>>
>> >>> On 3/10/19, 6:41 PM, Jiangli Zhou wrote:
>> >>>> Here is the updated webrev:
>> >>>> http://cr.openjdk.java.net/~jiangli/8220095/webrev.01/
>> >>>> <http://cr.openjdk.java.net/%7Ejiangli/8220095/webrev.01/>.
>> >>>>
>> >>>> - Incorporated all suggestions except the test platforms for
>> >>>> ModulesSymLink.java. I changed to requires linux, mac
>> and solaris
>> >>>> explicitly instead to avoid any potential issue with other
>> >>>> non-mainline testing platforms.
>> >>>> - Reverted the changes in sharedPathsMiscInfo.cpp.
>> Further testing
>> >>>> showed SharedPathsMiscInfo::check() were dealing the
>> system boot path
>> >>>> string set up by os::set_boot_path. Lois comments
>> reminded me to
>> >>>> double check with this. Thanks!
>> >>>>
>> >>>> Please help fire tier2 and tier3 runs with mach5.
>> >>> I ran tier2 and tier3 tests with your latest changes and
>> saw no test
>> >>> failures.
>> >>>
>> >> Great, thanks a lot!
>> >>
>> >>
>> >>> BTW, I was unable to download the jdk.patch - got "403 -
>> forbidden"
>> >>> error.
>> >>> Same error was seen with individual patch files.
>> >>> I used wget to get all the raw files into my repo and
>> then submitted
>> >>> the
>> >>> build and test job.
>> >>> Could you check the file permissions?
>> >>>
>> >> Yes, that's the file permission issue. I fixed the
>> permission for the
>> >> jdk.patch.
>> >>
>> >> Thanks!
>> >> Jiangli
>> >>
>> >>
>> >>> thanks,
>> >>> Calvin
>> >>>> Thanks!
>> >>>> Jiangli
>> >>>>
>> >>>> On Thu, Mar 7, 2019 at 5:11 AM Lois Foltan
>> <lois.foltan at oracle.com <mailto:lois.foltan at oracle.com>
>> >>>> <mailto:lois.foltan at oracle.com
>> <mailto:lois.foltan at oracle.com>>> wrote:
>> >>>>
>> >>>> On 3/6/2019 6:20 PM, Jiangli Zhou wrote:
>> >>>> > Please review the following fix for 8220095.
>> >>>> >
>> >>>> > webrev:
>> http://cr.openjdk.java.net/~jiangli/8220095/webrev.00/
>> >>>> <http://cr.openjdk.java.net/%7Ejiangli/8220095/webrev.00/>
>> >>>> > bug: https://bugs.openjdk.java.net/browse/JDK-8220095
>> >>>> >
>> >>>> > Symbolic links may be used commonly in some cloud
>> environments.
>> >>>> The target
>> >>>> > files might have different names than the linked
>> names. The VM
>> >>>> crashes when
>> >>>> > 'lib/modules' links to a target file with a
>> different name, for
>> >>>> example,
>> >>>> > lib/modules -> lib/0.
>> >>>> >
>> >>>> > The usage of the hard-coded MODULES_IMAGE_NAME
>> (used by
>> >>>> > ClassLoader::is_modules_image(const char*)) can
>> become
>> >>>> problematic in this
>> >>>> > case and leads to assertion failures and crashes
>> in this
>> >>>> case. The
>> >>>> > is_modules_image()
>> >>>> > checks always fail even the actual file is the
>> runtime image
>> >>>> because the
>> >>>> > canonical paths (which might not end with
>> 'modules') are passed
>> >>>> in for the
>> >>>> > check. The fix is to obtain the real name from
>> the canonical
>> >>>> path early
>> >>>> > during initialization and use that for the
>> is_modules_image()
>> >>> check.
>> >>>> >
>> >>>> > Tested with submit repo testing, tier1, tier2,
>> and hotspot
>> >>>> runtime tests
>> >>>> > locally.
>> >>>> >
>> >>>> > Thanks!
>> >>>> > Jiangli
>> >>>>
>> >>>> Hi Jiangli,
>> >>>>
>> >>>> This change looks good! A couple of minor comments:
>> >>>>
>> >>>> - classLoader.hpp
>> >>>> line #39 - I think you should expand on the
>> comment and add
>> >>>> why in
>> >>>> the case of the canonical path name
>> MODULES_IMAGE_NAME can not be
>> >>>> used
>> >>>> as-is but if one is dealing with the system boot
>> path string set
>> >>>> up by
>> >>>> os::set_boot_path, than MODULES_IMAGE_NAME should
>> be used.
>> >>>>
>> >>>> - classLoader.cpp
>> >>>> line #702 - Can you add the same explanation
>> comment as in
>> >>>> classLoader.hpp ahead of the new
>> >>>> ClassLoader::init_modules_image_name()
>> >>>> method? That would be helpful.
>> >>>> line #710 - ahead of setting
>> _modules_image_name please
>> >>>> consider
>> >>>> adding an assert that p1's length is greater than 0?
>> >>>> Maybe there should there be an error case
>> >>>> test
>> >>>> where "lib/modules -> lib/"
>> >>>>
>> >>>> Thanks,
>> >>>> Lois
>> >>>>
>> >>>> -
>> >>>>
>> >
>>
>
More information about the hotspot-runtime-dev
mailing list