linux-kernel - Re: [GIT PULL] Security subsystem updates for 4.14

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Date:   Fri, 8 Sep 2017 00:09:43 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     James Morris <jmorris@...ei.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [GIT PULL] Security subsystem updates for 4.14

The reason why I send out the original version of this patch
is because IMA used to call ->read under i_rwsem, and that deadlocked
on XFS and NFS, or ext3/4 with DAX.  The call path for that is

process_measurement (takes i_rwsem)
  -> ima_collect_measurement
    -> ima_calc_file_hash
       -> ima_calc_file_ahash / ima_calc_file_shash
         -> ima_calc_file_hash_atfm / ima_calc_file_hash_tfm
	   -> integrity_kernel_read

ima_check_last_writer (takes i_rwsem)
  -> ima_update_xattr
    -> ima_collect_measurement
       -> (as above)

But yes, for the init-time integrity_read_file this is incorrect.
It never tripped up, and I explicitly added the lockdep annotations
so that anything would show up, and it's been half a year since
I sent that first RFC patch..