On Tue, Apr 7, 2020 at 12:06 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > > On 4/5/20 8:06 PM, syzbot wrote: > > Hello, > > > > syzbot found the following crash on: > > > > HEAD commit: 1a323ea5 x86: get rid of 'errret' argument to __get_user_x.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=132e940be00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=8c1e98458335a7d1 > > dashboard link: https://syzkaller.appspot.com/bug?extid=d6ec23007e951dadf3de > > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12921933e00000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=172e940be00000 > > > > The bug was bisected to: > > > > commit e950564b97fd0f541b02eb207685d0746f5ecf29 > > Author: Miklos Szeredi <mszeredi@xxxxxxxxxx> > > Date: Tue Jul 24 13:01:55 2018 +0000 > > > > vfs: don't evict uninitialized inode > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=115cad33e00000 > > final crash: https://syzkaller.appspot.com/x/report.txt?x=135cad33e00000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=155cad33e00000 > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > Reported-by: syzbot+d6ec23007e951dadf3de@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: e950564b97fd ("vfs: don't evict uninitialized inode") > > > > overlayfs: upper fs does not support xattr, falling back to index=off and metacopy=off. > > ------------[ cut here ]------------ > > kernel BUG at mm/hugetlb.c:3416! > > invalid opcode: 0000 [#1] PREEMPT SMP KASAN > > CPU: 0 PID: 7036 Comm: syz-executor110 Not tainted 5.6.0-syzkaller #0 > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > RIP: 0010:__unmap_hugepage_range+0xa26/0xbc0 mm/hugetlb.c:3416 > > Code: 00 48 c7 c7 60 37 35 88 e8 57 b4 a2 ff e9 b3 fd ff ff e8 cd 90 c6 ff 0f 0b e9 c4 f7 ff ff e8 c1 90 c6 ff 0f 0b e8 ba 90 c6 ff <0f> 0b e8 b3 90 c6 ff 83 8c 24 c0 00 00 00 01 48 8d bc 24 a0 00 00 > > RSP: 0018:ffffc900017779b0 EFLAGS: 00010293 > > RAX: ffff88808cf5c2c0 RBX: ffffffff8c641c08 RCX: ffffffff81ac50b4 > > RDX: 0000000000000000 RSI: ffffffff81ac58a6 RDI: 0000000000000007 > > RBP: 0000000020000000 R08: ffff88808cf5c2c0 R09: ffffed10129d8111 > > R10: ffffed10129d8110 R11: ffff888094ec0887 R12: 0000000000003000 > > R13: 0000000000000000 R14: 0000000020003000 R15: 0000000000200000 > > FS: 00000000013c0880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000000020000140 CR3: 0000000093554000 CR4: 00000000001406f0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > __unmap_hugepage_range_final+0x30/0x70 mm/hugetlb.c:3507 > > unmap_single_vma+0x238/0x300 mm/memory.c:1296 > > unmap_vmas+0x16f/0x2f0 mm/memory.c:1332 > > exit_mmap+0x2aa/0x510 mm/mmap.c:3126 > > __mmput kernel/fork.c:1082 [inline] > > mmput+0x168/0x4b0 kernel/fork.c:1103 > > exit_mm kernel/exit.c:477 [inline] > > do_exit+0xa51/0x2dd0 kernel/exit.c:780 > > do_group_exit+0x125/0x340 kernel/exit.c:891 > > __do_sys_exit_group kernel/exit.c:902 [inline] > > __se_sys_exit_group kernel/exit.c:900 [inline] > > __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:900 > > do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 > > entry_SYSCALL_64_after_hwframe+0x49/0xb3 > > This is not new and certainly not caused by commit e950564b97fd. Sorry for replying late... > hugetlbf only operates on huge page aligned and sized files/mappings. > To make sure this happens, the mmap code contians the following to 'round > up' length to huge page size: > > if (!(flags & MAP_ANONYMOUS)) { > audit_mmap_fd(fd, flags); > file = fget(fd); > if (!file) > return -EBADF; > if (is_file_hugepages(file)) > len = ALIGN(len, huge_page_size(hstate_file(file))); > retval = -EINVAL; > if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file))) > goto out_fput; > } else if (flags & MAP_HUGETLB) { > struct user_struct *user = NULL; > struct hstate *hs; > > hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK); > if (!hs) > return -EINVAL; > > len = ALIGN(len, huge_page_size(hs)); > > However, in this syzbot test case the 'file' is in an overlayfs filesystem > created as follows: > > mkdir("./file0", 000) = 0 > mount(NULL, "./file0", "hugetlbfs", MS_MANDLOCK|MS_POSIXACL, NULL) = 0 > chdir("./file0") = 0 > mkdir("./file1", 000) = 0 > mkdir("./bus", 000) = 0 > mkdir("./file0", 000) = 0 > mount("\177ELF\2\1\1", "./bus", "overlay", 0, "lowerdir=./bus,workdir=./file1,u"...) = 0 > > The routine is_file_hugepages() is just comparing the file ops to huegtlbfs: > > if (file->f_op == &hugetlbfs_file_operations) > return true; > > Since the file is in an overlayfs, file->f_op == ovl_file_operations. > Therefore, length will not be rounded up to huge page size and we create a > mapping with incorrect size which leads to the BUG. > > Because of the code in mmap, the hugetlbfs mmap() routine assumes length is > rounded to a huge page size. I can easily add a check to hugetlbfs mmap > to validate length and return -EINVAL. However, I think we really want to > do the 'round up' earlier in mmap. This is because the man page says: > > Huge page (Huge TLB) mappings > For mappings that employ huge pages, the requirements for the arguments > of mmap() and munmap() differ somewhat from the requirements for map‐ > pings that use the native system page size. > > For mmap(), offset must be a multiple of the underlying huge page size. > The system automatically aligns length to be a multiple of the underly‐ > ing huge page size. > > Since the location for the mapping is chosen BEFORE getting to the hugetlbfs > mmap routine, we can not wait until then to round up the length. Is there a > defined way to go from a struct file * to the underlying filesystem so we > can continue to do the 'round up' in early mmap code? That's easy enough: static inline struct file *real_file(struct file *file) { return file->f_op != ovl_file_operations ? file : file->private_data; } But adding more filesystem specific code to generic code does not sound like the cleanest way to solve this... > One other thing I noticed with overlayfs is that it does not contain a > specific get_unmapped_area file_operations routine. I would expect it to at > least check for and use the get_unmapped_area of the underlying filesystem? > Can someone comment if this is by design? Not sure. What exactly is f_op->get_unmapped_area supposed to do? > In the case of hugetlbfs, get_unmapped_area is even provided by most > architectures. So, it seems like we would like/need to be calling the correct > routine. Okay. Thanks, Miklos
