On 4/30/18 9:02 AM, Dmitry Vyukov wrote: > On Mon, Apr 30, 2018 at 3:49 PM, Eric Sandeen <sandeen@xxxxxxxxxxx> wrote: ... >>> It just extracted kernel source file name that looked relevant >>> to this crash and run get_maintainers.pl on it. >>> Also the image can contain dynamically generated data, which makes it >>> impossible to have as a file at all. >> >> I guess I'm not sure what this means, can you explain? > > Say, a value that we generally pass to close system call is not static > and can't be dumped to a static file. It's whatever a previous open > system call has returned. Inside of the program we memorize the return > value of open in a variable and then pass it to close. This generally > stands for all system calls. Say, an image can contain an uid, and > that uid can be obtained from a system call too. Ok, but that's the syscall side. You are operating on a static xfs image, correct? We're only asking for the actual filesystem you're operating against. (When I say "image" I am talking only about the filesystem itself, not any other syzkaller state) ... >> That was not at all clear to me. I thought when syzkaller was telling us >> "on upstream commit XYZ," it meant that it had identified commit XYZ as bad. >> I'm not sure if anyone else made that mistake, but perhaps you could also clarify >> the bug report text in this regard? > > Suggestions are welcome. Currently it says "syzbot hit the following > crash on upstream commit SHA1", which was supposed to mean just the > state of the source tree when the crash happened. But I am not a > native speaker, so perhaps I am saying not what I intend to say. > > There are also suggestions on report format improvement from +Ted > currently in works: > https://github.com/google/syzkaller/issues/565#issuecomment-380792942 > Not sure if they make this distinction 100% clear, though. Maybe I was the only one who misunderstood, but something like git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git HEAD: f5c754d63d06 mm/swap_state.c: make bool enable_vma_readahead and swap_vma_readahead() to make it clear that it has not identified that commit as the culprit, it's just the head of the tree you were testing? (I think I have the correct git nomenclature ...) ... >> If the base image only has one allocation group, it makes it more difficult for >> some tools to work with the image, because there is no redundancy. 1 AG is >> not a supported or recommended geometry for any real-life use of xfs. >> >> If I am correct that you start with a base image w/ a certain geometry or >> set of mkfs options, starting with >= 2 AGs would improve the usefulness of the >> filesystem image. > > syzkaller can generate/mutate images based on structured format > templates, but for now we don't have any templates and these are just > opaque blobs. Ok, backing up more: When you are testing against an xfs filesystem image, where does that image come from? How is it generated? A quick look at the syzkaller tree didn't make that clear to me. the xfs.repro file you provided at https://drive.google.com/file/d/1jzhGGe5SBJcqfsjxCLHoh4Kazke1oTfC/view is strange, it doesn't even contain AGF blocks; they aren't fuzzed or corrupted, they are completely zeroed out. I don't know if that's part of the fuzzing, or what - what steps led to that image? Or put another way, how did you arrive at the fs image values in the reproducer, i.e.: oid loop() { memcpy((void*)0x20000000, "xfs", 4); memcpy((void*)0x20000100, "./file0", 8); *(uint64_t*)0x20000200 = 0x20010000; memcpy((void*)0x20010000, "\x58\x46\x53\x42\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x10\x00\x00" "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x9f\x98" "\x99\xff\xcb\xa1\x4e\xe6\xad\x52\x08\x20\x67\x09\xed\x75\x00\x00\x00" "\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x35\xe0\x00\x00\x00\x00" "\x00\x00\x35\xe1\x00\x00\x00\x00\x00\x00\x35\xe2\x00\x00\x00\x01\x00" "\x00\x10\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x03\x55\xb4\xa4" "\x02\x00\x01\x00\x00\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" "\x00\x0c\x09\x08\x04\x0c\x00\x00\x19\x00\x00\x00\x00\x00\x00\x00\x40" "\x00\x00\x00\x00\x00\x00\x00\x3d\x00\x00\x00\x00\x00\x00\x0c\xa3\x00" "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00" "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x02\x02", 204); ... The in-memory xfs filesystem it constructs is damaged, is that an intentional part of the fuzzing during the test? -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
