• Laura Abbott's avatar
    mm: slub: Fix slab walking for init_on_free · 1b7e816f
    Laura Abbott authored
    To properly clear the slab on free with slab_want_init_on_free, we walk
    the list of free objects using get_freepointer/set_freepointer.
    
    The value we get from get_freepointer may not be valid.  This isn't an
    issue since an actual value will get written later but this means
    there's a chance of triggering a bug if we use this value with
    set_freepointer:
    
      kernel BUG at mm/slub.c:306!
      invalid opcode: 0000 [#1] PREEMPT PTI
      CPU: 0 PID: 0 Comm: swapper Not tainted 5.2.0-05754-g6471384a #4
      RIP: 0010:kfree+0x58a/0x5c0
      Code: 48 83 05 78 37 51 02 01 0f 0b 48 83 05 7e 37 51 02 01 48 83 05 7e 37 51 02 01 48 83 05 7e 37 51 02 01 48 83 05 d6 37 51 02 01 <0f> 0b 48 83 05 d4 37 51 02 01 48 83 05 d4 37 51 02 01 48 83 05 d4
      RSP: 0000:ffffffff82603d90 EFLAGS: 00010002
      RAX: ffff8c3976c04320 RBX: ffff8c3976c04300 RCX: 0000000000000000
      RDX: ffff8c3976c04300 RSI: 0000000000000000 RDI: ffff8c3976c04320
      RBP: ffffffff82603db8 R08: 0000000000000000 R09: 0000000000000000
      R10: ffff8c3976c04320 R11: ffffffff8289e1e0 R12: ffffd52cc8db0100
      R13: ffff8c3976c01a00 R14: ffffffff810f10d4 R15: ffff8c3976c04300
      FS:  0000000000000000(0000) GS:ffffffff8266b000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: ffff8c397ffff000 CR3: 0000000125020000 CR4: 00000000000406b0
      Call Trace:
       apply_wqattrs_prepare+0x154/0x280
       apply_workqueue_attrs_locked+0x4e/0xe0
       apply_workqueue_attrs+0x36/0x60
       alloc_workqueue+0x25a/0x6d0
       workqueue_init_early+0x246/0x348
       start_kernel+0x3c7/0x7ec
       x86_64_start_reservations+0x40/0x49
       x86_64_start_kernel+0xda/0xe4
       secondary_startup_64+0xb6/0xc0
      Modules linked in:
      ---[ end trace f67eb9af4d8d492b ]---
    
    Fix this by ensuring the value we set with set_freepointer is either NULL
    or another value in the chain.
    Reported-by: default avatarkernel test robot <rong.a.chen@intel.com>
    Signed-off-by: default avatarLaura Abbott <labbott@redhat.com>
    Fixes: 6471384a ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
    Reviewed-by: default avatarKees Cook <keescook@chromium.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    1b7e816f