1. 22 Jan, 2014 34 commits
  2. 13 Jan, 2014 4 commits
  3. 12 Jan, 2014 2 commits
    • Linus Torvalds's avatar
      Linux 3.13-rc8 · 7e22e911
      Linus Torvalds authored
      7e22e911
    • Steven Rostedt's avatar
      SELinux: Fix possible NULL pointer dereference in selinux_inode_permission() · 3dc91d43
      Steven Rostedt authored
      While running stress tests on adding and deleting ftrace instances I hit
      this bug:
      
        BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
        IP: selinux_inode_permission+0x85/0x160
        PGD 63681067 PUD 7ddbe067 PMD 0
        Oops: 0000 [#1] PREEMPT
        CPU: 0 PID: 5634 Comm: ftrace-test-mki Not tainted 3.13.0-rc4-test-00033-gd2a6dde-dirty #20
        Hardware name:                  /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006
        task: ffff880078375800 ti: ffff88007ddb0000 task.ti: ffff88007ddb0000
        RIP: 0010:[<ffffffff812d8bc5>]  [<ffffffff812d8bc5>] selinux_inode_permission+0x85/0x160
        RSP: 0018:ffff88007ddb1c48  EFLAGS: 00010246
        RAX: 0000000000000000 RBX: 0000000000800000 RCX: ffff88006dd43840
        RDX: 0000000000000001 RSI: 0000000000000081 RDI: ffff88006ee46000
        RBP: ffff88007ddb1c88 R08: 0000000000000000 R09: ffff88007ddb1c54
        R10: 6e6576652f6f6f66 R11: 0000000000000003 R12: 0000000000000000
        R13: 0000000000000081 R14: ffff88006ee46000 R15: 0000000000000000
        FS:  00007f217b5b6700(0000) GS:ffffffff81e21000(0000) knlGS:0000000000000000
        CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M
        CR2: 0000000000000020 CR3: 000000006a0fe000 CR4: 00000000000007f0
        Call Trace:
          security_inode_permission+0x1c/0x30
          __inode_permission+0x41/0xa0
          inode_permission+0x18/0x50
          link_path_walk+0x66/0x920
          path_openat+0xa6/0x6c0
          do_filp_open+0x43/0xa0
          do_sys_open+0x146/0x240
          SyS_open+0x1e/0x20
          system_call_fastpath+0x16/0x1b
        Code: 84 a1 00 00 00 81 e3 00 20 00 00 89 d8 83 c8 02 40 f6 c6 04 0f 45 d8 40 f6 c6 08 74 71 80 cf 02 49 8b 46 38 4c 8d 4d cc 45 31 c0 <0f> b7 50 20 8b 70 1c 48 8b 41 70 89 d9 8b 78 04 e8 36 cf ff ff
        RIP  selinux_inode_permission+0x85/0x160
        CR2: 0000000000000020
      
      Investigating, I found that the inode->i_security was NULL, and the
      dereference of it caused the oops.
      
      in selinux_inode_permission():
      
      	isec = inode->i_security;
      
      	rc = avc_has_perm_noaudit(sid, isec->sid, isec->sclass, perms, 0, &avd);
      
      Note, the crash came from stressing the deletion and reading of debugfs
      files.  I was not able to recreate this via normal files.  But I'm not
      sure they are safe.  It may just be that the race window is much harder
      to hit.
      
      What seems to have happened (and what I have traced), is the file is
      being opened at the same time the file or directory is being deleted.
      As the dentry and inode locks are not held during the path walk, nor is
      the inodes ref counts being incremented, there is nothing saving these
      structures from being discarded except for an rcu_read_lock().
      
      The rcu_read_lock() protects against freeing of the inode, but it does
      not protect freeing of the inode_security_struct.  Now if the freeing of
      the i_security happens with a call_rcu(), and the i_security field of
      the inode is not changed (it gets freed as the inode gets freed) then
      there will be no issue here.  (Linus Torvalds suggested not setting the
      field to NULL such that we do not need to check if it is NULL in the
      permission check).
      
      Note, this is a hack, but it fixes the problem at hand.  A real fix is
      to restructure the destroy_inode() to call all the destructor handlers
      from the RCU callback.  But that is a major job to do, and requires a
      lot of work.  For now, we just band-aid this bug with this fix (it
      works), and work on a more maintainable solution in the future.
      
      Link: http://lkml.kernel.org/r/20140109101932.0508dec7@gandalf.local.home
      Link: http://lkml.kernel.org/r/20140109182756.17abaaa8@gandalf.local.home
      
      Cc: stable@vger.kernel.org
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      3dc91d43