On Thu, Jun 24, 2021 at 7:28 PM Rustam Kovhaev <rkovhaev@xxxxxxxxx> wrote: > > > > On Wed, Apr 7, 2021 at 4:24 PM Rustam Kovhaev <rkovhaev@xxxxxxxxx> wrote: > > > > > > > > > > On Mon, Mar 01, 2021 at 09:43:00PM +0100, Dmitry Vyukov wrote: > > > > > > On Mon, Mar 1, 2021 at 9:39 PM Rustam Kovhaev <rkovhaev@xxxxxxxxx> wrote: > > > > > > > > > > > > > > On Mon, Mar 01, 2021 at 08:05:42PM +0100, Dmitry Vyukov wrote: > > > > > > > > On Mon, Mar 1, 2021 at 5:21 PM Rustam Kovhaev <rkovhaev@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > On Wed, Dec 09, 2020 at 10:58:10PM -0800, syzbot wrote: > > > > > > > > > > syzbot has found a reproducer for the following issue on: > > > > > > > > > > > > > > > > > > > > HEAD commit: a68a0262 mm/madvise: remove racy mm ownership check > > > > > > > > > > git tree: upstream > > > > > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=11facf17500000 > > > > > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=4305fa9ea70c7a9f > > > > > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=f3694595248708227d35 > > > > > > > > > > compiler: gcc (GCC) 10.1.0-syz 20200507 > > > > > > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=159a9613500000 > > > > > > > > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11bf7123500000 > > > > > > > > > > > > > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > > > > > > > > Reported-by: syzbot+f3694595248708227d35@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > > > > > > > > > > > > > > > > > Debian GNU/Linux 9 syzkaller ttyS0 > > > > > > > > > > Warning: Permanently added '10.128.0.9' (ECDSA) to the list of known hosts. > > > > > > > > > > executing program > > > > > > > > > > executing program > > > > > > > > > > executing program > > > > > > > > > > BUG: memory leak > > > > > > > > > > unreferenced object 0xffff88810efccc80 (size 64): > > > > > > > > > > comm "syz-executor334", pid 8460, jiffies 4294945724 (age 13.850s) > > > > > > > > > > hex dump (first 32 bytes): > > > > > > > > > > c0 cb 14 04 00 ea ff ff c0 c2 11 04 00 ea ff ff ................ > > > > > > > > > > c0 56 3f 04 00 ea ff ff 40 18 38 04 00 ea ff ff .V?.....@.8..... > > > > > > > > > > backtrace: > > > > > > > > > > [<0000000036ae98a7>] kmalloc_node include/linux/slab.h:575 [inline] > > > > > > > > > > [<0000000036ae98a7>] bpf_ringbuf_area_alloc kernel/bpf/ringbuf.c:94 [inline] > > > > > > > > > > [<0000000036ae98a7>] bpf_ringbuf_alloc kernel/bpf/ringbuf.c:135 [inline] > > > > > > > > > > [<0000000036ae98a7>] ringbuf_map_alloc kernel/bpf/ringbuf.c:183 [inline] > > > > > > > > > > [<0000000036ae98a7>] ringbuf_map_alloc+0x1be/0x410 kernel/bpf/ringbuf.c:150 > > > > > > > > > > [<00000000d2cb93ae>] find_and_alloc_map kernel/bpf/syscall.c:122 [inline] > > > > > > > > > > [<00000000d2cb93ae>] map_create kernel/bpf/syscall.c:825 [inline] > > > > > > > > > > [<00000000d2cb93ae>] __do_sys_bpf+0x7d0/0x30a0 kernel/bpf/syscall.c:4381 > > > > > > > > > > [<000000008feaf393>] do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46 > > > > > > > > > > [<00000000e1f53cfd>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > i am pretty sure that this one is a false positive > > > > > > > > > the problem with reproducer is that it does not terminate all of the > > > > > > > > > child processes that it spawns > > > > > > > > > > > > > > > > > > i confirmed that it is a false positive by tracing __fput() and > > > > > > > > > bpf_map_release(), i ran reproducer, got kmemleak report, then i > > > > > > > > > manually killed those running leftover processes from reproducer and > > > > > > > > > then both functions were executed and memory was freed > > > > > > > > > > > > > > > > > > i am marking this one as: > > > > > > > > > #syz invalid > > > > > > > > > > > > > > > > Hi Rustam, > > > > > > > > > > > > > > > > Thanks for looking into this. > > > > > > > > > > > > > > > > I wonder how/where are these objects referenced? If they are not > > > > > > > > leaked and referenced somewhere, KMEMLEAK should not report them as > > > > > > > > leaks. > > > > > > > > So even if this is a false positive for BPF, this is a true positive > > > > > > > > bug and something to fix for KMEMLEAK ;) > > > > > > > > And syzbot will probably re-create this bug report soon as this still > > > > > > > > happens and is not a one-off thing. > > > > > > > > > > > > > > hi Dmitry, i haven't thought of it this way, but i guess you are right, > > > > > > > it is a kmemleak bug, ideally kmemleak should be aware that there are > > > > > > > still running processes holding references to bpf fd/anonymous inodes > > > > > > > which in their turn hold references to allocated bpf maps > > > > > > > > > > > > KMEMLEAK scans whole memory, so if there are pointers to the object > > > > > > anywhere in memory, KMEMLEAK should not report them as leaked. Running > > > > > > processes have no direct effect on KMEMLEAK logic. > > > > > > So the question is: where are these pointers to these objects? If we > > > > > > answer this, we can check how/why KMEMLEAK misses them. Are they > > > > > > mangled in some way? > > > > > thank you for your comments, they make sense, and indeed, the pointer > > > > > gets vmaped. > > > > > i should have looked into this sooner, becaused syzbot did trigger the > > > > > issue again, and Andrii had to look into the same bug, sorry about that. > > > > > > > > No worries! I actually forgot about this thread :) Let's leave the > > > > link to my today's investigation ([0]) just for completeness. > > > > > > > > [0] https://lore.kernel.org/bpf/CAEf4BzYk+dqs+jwu6VKXP-RttcTEGFe+ySTGWT9CRNkagDiJVA@xxxxxxxxxxxxxx/ > > > > > > > > > if i am understanding this correctly here is what the fix should be: > > > > > --- > > > > > kernel/bpf/ringbuf.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c > > > > > index f25b719ac786..30400e74abe2 100644 > > > > > --- a/kernel/bpf/ringbuf.c > > > > > +++ b/kernel/bpf/ringbuf.c > > > > > @@ -8,6 +8,7 @@ > > > > > #include <linux/vmalloc.h> > > > > > #include <linux/wait.h> > > > > > #include <linux/poll.h> > > > > > +#include <linux/kmemleak.h> > > > > > #include <uapi/linux/btf.h> > > > > > > > > > > #define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE) > > > > > @@ -105,6 +106,7 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node) > > > > > rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages, > > > > > VM_ALLOC | VM_USERMAP, PAGE_KERNEL); > > > > > if (rb) { > > > > > + kmemleak_not_leak((void *) pages); > > > > > > > > If that makes kmemleak happy, I have no problems with this. But maybe > > > > leave some comment explaining why this is needed at all? > > > > > > > > And for my understanding, how vmap changes anything? Those pages are > > > > still referenced from rb, which is referenced from some struct file in > > > > the system. Sorry if that's a naive question. > > > > > > > valid question, it does look like kmemleak should be scanning > > > vmalloc()/vmap() memory, i will research this further > > > > a quick update, i see a problem in kmemleak code, and i have simplified > > the reproducer by getting rid of a vmap(). > > i will reach out to maintainer and mm and afterwards i will update this > > bug, cheers! > > > > Andrii, we have discovered that kmemleak scans struct page, but it does > not scan page contents and this is by design. if we allocate some memory > with kmalloc(), then allocate page with alloc_page(), and if we put > kmalloc pointer somewhere inside that page, kmemleak will report kmalloc > pointer as a false positive. > we can instruct kmemleak to scan the memory area by calling > kmemleak_alloc()/kmemleak_free() as shown below. if we don't need that > memory to be scanned then we can use kmemleak_not_leak(). > if we use the former then i guess we need to be careful since we do not > want/need to scan the memory that is being used by user-space. Thanks for your heroic digging and persistence on this issue, Rustam! > --- > kernel/bpf/ringbuf.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c > index 84b3b35fc0d0..cf7ce10b4fb1 100644 > --- a/kernel/bpf/ringbuf.c > +++ b/kernel/bpf/ringbuf.c > @@ -8,6 +8,7 @@ > #include <linux/vmalloc.h> > #include <linux/wait.h> > #include <linux/poll.h> > +#include <linux/kmemleak.h> > #include <uapi/linux/btf.h> > > #define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE) > @@ -105,6 +106,7 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node) > rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages, > VM_ALLOC | VM_USERMAP, PAGE_KERNEL); > if (rb) { > + kmemleak_alloc(rb, PAGE_SIZE, 1, flags); > rb->pages = pages; > rb->nr_pages = nr_pages; > return rb; > @@ -184,6 +186,7 @@ static void bpf_ringbuf_free(struct bpf_ringbuf *rb) > struct page **pages = rb->pages; > int i, nr_pages = rb->nr_pages; > > + kmemleak_free(rb); > vunmap(rb); > for (i = 0; i < nr_pages; i++) > __free_page(pages[i]); > -- > 2.30.2 >
