• Michal Hocko's avatar
    mm: do not bug_on on incorrect length in __mm_populate() · bb177a73
    Michal Hocko authored
    syzbot has noticed that a specially crafted library can easily hit
    VM_BUG_ON in __mm_populate
    
      kernel BUG at mm/gup.c:1242!
      invalid opcode: 0000 [#1] SMP
      CPU: 2 PID: 9667 Comm: a.out Not tainted 4.18.0-rc3 #644
      Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
      RIP: 0010:__mm_populate+0x1e2/0x1f0
      Code: 55 d0 65 48 33 14 25 28 00 00 00 89 d8 75 21 48 83 c4 20 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 75 18 f1 ff 0f 0b e8 6e 18 f1 ff <0f> 0b 31 db eb c9 e8 93 06 e0 ff 0f 1f 00 55 48 89 e5 53 48 89 fb
      Call Trace:
         vm_brk_flags+0xc3/0x100
         vm_brk+0x1f/0x30
         load_elf_library+0x281/0x2e0
         __ia32_sys_uselib+0x170/0x1e0
         do_fast_syscall_32+0xca/0x420
         entry_SYSENTER_compat+0x70/0x7f
    
    The reason is that the length of the new brk is not page aligned when we
    try to populate the it.  There is no reason to bug on that though.
    do_brk_flags already aligns the length properly so the mapping is
    expanded as it should.  All we need is to tell mm_populate about it.
    Besides that there is absolutely no reason to to bug_on in the first
    place.  The worst thing that could happen is that the last page wouldn't
    get populated and that is far from putting system into an inconsistent
    state.
    
    Fix the issue by moving the length sanitization code from do_brk_flags
    up to vm_brk_flags.  The only other caller of do_brk_flags is brk
    syscall entry and it makes sure to provide the proper length so t here
    is no need for sanitation and so we can use do_brk_flags without it.
    
    Also remove the bogus BUG_ONs.
    
    [osalvador@techadventures.net: fix up vm_brk_flags s@request@len@]
    Link: http://lkml.kernel.org/r/20180706090217.GI32658@dhcp22.suse.czSigned-off-by: 's avatarMichal Hocko <mhocko@suse.com>
    Reported-by: 's avatarsyzbot <syzbot+5dcb560fe12aa5091c06@syzkaller.appspotmail.com>
    Tested-by: 's avatarTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Reviewed-by: 's avatarOscar Salvador <osalvador@suse.de>
    Cc: Zi Yan <zi.yan@cs.rutgers.edu>
    Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    Cc: Michael S. Tsirkin <mst@redhat.com>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: "Huang, Ying" <ying.huang@intel.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    bb177a73