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? 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
