• zhong jiang's avatar
    mm/mempolicy: fix use after free when calling get_mempolicy · 6b2676ed
    zhong jiang authored
    commit 73223e4e upstream.
    
    I hit a use after free issue when executing trinity and repoduced it
    with KASAN enabled.  The related call trace is as follows.
    
      BUG: KASan: use after free in SyS_get_mempolicy+0x3c8/0x960 at addr ffff8801f582d766
      Read of size 2 by task syz-executor1/798
    
      INFO: Allocated in mpol_new.part.2+0x74/0x160 age=3 cpu=1 pid=799
         __slab_alloc+0x768/0x970
         kmem_cache_alloc+0x2e7/0x450
         mpol_new.part.2+0x74/0x160
         mpol_new+0x66/0x80
         SyS_mbind+0x267/0x9f0
         system_call_fastpath+0x16/0x1b
      INFO: Freed in __mpol_put+0x2b/0x40 age=4 cpu=1 pid=799
         __slab_free+0x495/0x8e0
         kmem_cache_free+0x2f3/0x4c0
         __mpol_put+0x2b/0x40
         SyS_mbind+0x383/0x9f0
         system_call_fastpath+0x16/0x1b
      INFO: Slab 0xffffea0009cb8dc0 objects=23 used=8 fp=0xffff8801f582de40 flags=0x200000000004080
      INFO: Object 0xffff8801f582d760 @offset=5984 fp=0xffff8801f582d600
    
      Bytes b4 ffff8801f582d750: ae 01 ff ff 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
      Object ffff8801f582d760: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b  kkkkkkkkkkkkkkkk
      Object ffff8801f582d770: 6b 6b 6b 6b 6b 6b 6b a5                          kkkkkkk.
      Redzone ffff8801f582d778: bb bb bb bb bb bb bb bb                          ........
      Padding ffff8801f582d8b8: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
      Memory state around the buggy address:
      ffff8801f582d600: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc
      ffff8801f582d680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
      >ffff8801f582d700: fc fc fc fc fc fc fc fc fc fc fc fc fb fb fb fc
    
    !shared memory policy is not protected against parallel removal by other
    thread which is normally protected by the mmap_sem.  do_get_mempolicy,
    however, drops the lock midway while we can still access it later.
    
    Early premature up_read is a historical artifact from times when
    put_user was called in this path see https://lwn.net/Articles/124754/
    but that is gone since 8bccd85f ("[PATCH] Implement sys_* do_*
    layering in the memory policy layer.").  but when we have the the
    current mempolicy ref count model.  The issue was introduced
    accordingly.
    
    Fix the issue by removing the premature release.
    
    Link: http://lkml.kernel.org/r/1502950924-27521-1-git-send-email-zhongjiang@huawei.comSigned-off-by: default avatarzhong jiang <zhongjiang@huawei.com>
    Acked-by: default avatarMichal Hocko <mhocko@suse.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Mel Gorman <mgorman@techsingularity.net>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    6b2676ed
mempolicy.c 71.2 KB