Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with smack enabled environment

From	Al Viro <viro@ZenIV.linux.org.uk>
Newsgroups	linux.kernel
Subject	Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with smack enabled environment
Date	2016-05-27 21:40 +0200
Message-ID	<rDvLX-7wI-9@gated-at.bofh.it> (permalink)
References	<rDnOp-2G0-1@gated-at.bofh.it> <rDrIl-56a-3@gated-at.bofh.it> <rDv9g-74Q-13@gated-at.bofh.it> <rDviW-7nc-17@gated-at.bofh.it>
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On Fri, May 27, 2016 at 12:03:37PM -0700, Casey Schaufler wrote:

> I haven't actually seen the problem, but I've been having
> real trouble getting a systemd configuration working properly.
> The quickest validation will probably be coming from Seung-Woo Kim,
> who reported the issue initially. I am working to verify both the
> problem and the fix.

To trigger it you need to end up in smack_d_instantiate() for a directory
that had SMK_INODE_CHANGED set in smack_inode_init_security().  IOW,
smk_inode_transmutable() being true for its parent and smk_access_entry()
for that parent returning something with MAY_TRANSMUTE in it.

I'm not familiar enough with smack guts to put together a reproducer,
but *ANY* call of ->setxattr() from smack_d_instantiate() on xattr-supporting
filesystem will blow up in the mainline.  At that point dentry still has
NULL ->d_inode, so ->setxattr() instances are going to oops as soon as they
try to do anything with the inode.  All it takes is getting to that method
call.

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[BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Seung-Woo Kim <sw0312.kim@samsung.com> - 2016-05-27 13:10 +0200
  Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 17:20 +0200
    Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 21:00 +0200
      Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-27 21:10 +0200
        Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 21:30 +0200
          Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-27 21:40 +0200
            Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 21:50 +0200
              Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-27 21:50 +0200
                Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 22:30 +0200
                Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Casey Schaufler <casey@schaufler-ca.com> - 2016-05-28 00:50 +0200
                Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Seung-Woo Kim <sw0312.kim@samsung.com> - 2016-05-30 03:50 +0200
      Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path with  smack enabled environment Casey Schaufler <casey@schaufler-ca.com> - 2016-05-27 21:10 +0200
        Re: [BUG] Panic when systemd boot do mkdir on tmpfs mounted path  with smack enabled environment Al Viro <viro@ZenIV.linux.org.uk> - 2016-05-27 21:40 +0200

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