On Wed, Dec 19, 2018 at 2:23 PM Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 12/19/18 3:23 AM, Alexander Potapenko wrote: > > On Thu, Sep 13, 2018 at 11:23 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > >> > >> On Thu, Sep 13, 2018 at 11:18 AM syzbot > >> <syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > >>> > >>> Hello, > >>> > >>> syzbot found the following crash on: > >>> > >>> HEAD commit: 123906095e30 kmsan: introduce kmsan_interrupt_enter()/kmsa.. > >>> git tree: https://github.com/google/kmsan.git/master > >>> console output: https://syzkaller.appspot.com/x/log.txt?x=1249fcb8400000 > >>> kernel config: https://syzkaller.appspot.com/x/.config?x=848e40757852af3e > >>> dashboard link: https://syzkaller.appspot.com/bug?extid=2dcfeaf8cb49b05e8f1a > >>> compiler: clang version 7.0.0 (trunk 334104) > >>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=116ef050400000 > >>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=122870ff800000 > >>> > >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: > >>> Reported-by: syzbot+2dcfeaf8cb49b05e8f1a@xxxxxxxxxxxxxxxxxxxxxxxxx > >>> > >>> random: sshd: uninitialized urandom read (32 bytes read) > >>> ================================================================== > >>> BUG: KMSAN: kernel-infoleak in copyout lib/iov_iter.c:140 [inline] > >>> BUG: KMSAN: kernel-infoleak in copy_page_to_iter_iovec lib/iov_iter.c:212 > >>> [inline] > >>> BUG: KMSAN: kernel-infoleak in copy_page_to_iter+0x754/0x1b70 > >>> lib/iov_iter.c:716 > >>> CPU: 0 PID: 4516 Comm: blkid Not tainted 4.17.0+ #9 > >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > >>> Google 01/01/2011 > >>> Call Trace: > >>> __dump_stack lib/dump_stack.c:77 [inline] > >>> dump_stack+0x185/0x1d0 lib/dump_stack.c:113 > >>> kmsan_report+0x188/0x2a0 mm/kmsan/kmsan.c:1125 > >>> kmsan_internal_check_memory+0x17e/0x1f0 mm/kmsan/kmsan.c:1238 > >>> kmsan_copy_to_user+0x7a/0x160 mm/kmsan/kmsan.c:1261 > >>> copyout lib/iov_iter.c:140 [inline] > >>> copy_page_to_iter_iovec lib/iov_iter.c:212 [inline] > >>> copy_page_to_iter+0x754/0x1b70 lib/iov_iter.c:716 > >>> generic_file_buffered_read mm/filemap.c:2185 [inline] > >>> generic_file_read_iter+0x2ef8/0x44d0 mm/filemap.c:2362 > >>> blkdev_read_iter+0x20d/0x280 fs/block_dev.c:1930 > >>> call_read_iter include/linux/fs.h:1778 [inline] > >>> new_sync_read fs/read_write.c:406 [inline] > >>> __vfs_read+0x775/0x9d0 fs/read_write.c:418 > >>> vfs_read+0x36c/0x6b0 fs/read_write.c:452 > >>> ksys_read fs/read_write.c:578 [inline] > >>> __do_sys_read fs/read_write.c:588 [inline] > >>> __se_sys_read fs/read_write.c:586 [inline] > >>> __x64_sys_read+0x1bf/0x3e0 fs/read_write.c:586 > >>> do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287 > >>> entry_SYSCALL_64_after_hwframe+0x44/0xa9 > >>> RIP: 0033:0x7fdeff68f310 > >>> RSP: 002b:00007ffe999660b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > >>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fdeff68f310 > >>> RDX: 0000000000000100 RSI: 0000000001e78df8 RDI: 0000000000000003 > >>> RBP: 0000000001e78dd0 R08: 0000000000000028 R09: 0000000001680000 > >>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000001e78030 > >>> R13: 0000000000000100 R14: 0000000001e78080 R15: 0000000001e78de8 > >>> > >>> Uninit was created at: > >>> kmsan_save_stack_with_flags mm/kmsan/kmsan.c:282 [inline] > >>> kmsan_alloc_meta_for_pages+0x161/0x3a0 mm/kmsan/kmsan.c:819 > >>> kmsan_alloc_page+0x82/0xe0 mm/kmsan/kmsan.c:889 > >>> __alloc_pages_nodemask+0xf7b/0x5cc0 mm/page_alloc.c:4402 > >>> alloc_pages_current+0x6b1/0x970 mm/mempolicy.c:2093 > >>> alloc_pages include/linux/gfp.h:494 [inline] > >>> __page_cache_alloc+0x95/0x320 mm/filemap.c:946 > >>> pagecache_get_page+0x52b/0x1450 mm/filemap.c:1577 > >>> grab_cache_page_write_begin+0x10d/0x190 mm/filemap.c:3089 > >>> block_write_begin+0xf9/0x3a0 fs/buffer.c:2068 > >>> blkdev_write_begin+0xf5/0x110 fs/block_dev.c:584 > >>> generic_perform_write+0x438/0x9d0 mm/filemap.c:3139 > >>> __generic_file_write_iter+0x43b/0xa10 mm/filemap.c:3264 > >>> blkdev_write_iter+0x3a8/0x5f0 fs/block_dev.c:1910 > >>> do_iter_readv_writev+0x81c/0xa20 include/linux/fs.h:1778 > >>> do_iter_write+0x30d/0xd50 fs/read_write.c:959 > >>> vfs_writev fs/read_write.c:1004 [inline] > >>> do_writev+0x3be/0x820 fs/read_write.c:1039 > >>> __do_sys_writev fs/read_write.c:1112 [inline] > >>> __se_sys_writev fs/read_write.c:1109 [inline] > >>> __x64_sys_writev+0xe1/0x120 fs/read_write.c:1109 > >>> do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287 > >>> entry_SYSCALL_64_after_hwframe+0x44/0xa9 > >>> > >>> Bytes 4-255 of 256 are uninitialized > >>> Memory access starts at ffff8801b9903000 > >>> ================================================================== > >> This particular report was caused by the repro program writing a byte > >> to /dev/nullb0 and /sbin/blkid reading from that device in the > >> background. > >> But it turns out that simply running `cat /dev/nullb0` already prints > >> uninitialized kernel memory. > >> Is this the intended behavior of the null block driver? > > A friendly ping, this bug is still reproducible on syzbot. > > Does this fix it? There must be something wrong with my tool, as it stops reporting this bug when I apply your patch. However when I run `cat /dev/nullb0 | strings` and wait long enough I start seeing meaningful strings (file names, env dumps etc.) I suspect this is still unexpected, right? > > diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c > index 62c9654b9ce8..08808c572692 100644 > --- a/drivers/block/null_blk_main.c > +++ b/drivers/block/null_blk_main.c > @@ -655,7 +655,7 @@ static struct nullb_page *null_alloc_page(gfp_t gfp_flags) > if (!t_page) > goto out; > > - t_page->page = alloc_pages(gfp_flags, 0); > + t_page->page = alloc_pages(gfp_flags | __GFP_ZERO, 0); > if (!t_page->page) > goto out_freepage; > > > -- > Jens Axboe > -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
