Stable backport of de3004c874e7 ("ocfs2: Switch to security_inode_init_security()")

[Paul Moore]

Hello,

I would like to request the backport of the commit below to address a
kernel panic in ocfs2 that was identified by Valentin Vidić in this
thread:

https://lore.kernel.org/linux-security-module/20230401214151.1243189-1-vvidic@valentin-vidic.from.hr

While Valentin provides his own patch in the original message, the
preferred patch is one that went up to Linus during the last merge
window; Valentin has tested the patch and confirmed that it resolved
the reported problem.

  commit de3004c874e740304cc4f4a83d6200acb511bbda
  Author: Roberto Sassu <roberto.sassu at huawei.com>
  Date:   Tue Mar 14 09:17:16 2023 +0100

   ocfs2: Switch to security_inode_init_security()

   In preparation for removing security_old_inode_init_security(), switch to
   security_inode_init_security().

   Extend the existing ocfs2_initxattrs() to take the
   ocfs2_security_xattr_info structure from fs_info, and populate the
   name/value/len triple with the first xattr provided by LSMs.

   As fs_info was not used before, ocfs2_initxattrs() can now handle the case
   of replicating the behavior of security_old_inode_init_security(), i.e.
   just obtaining the xattr, in addition to setting all xattrs provided by
   LSMs.

   Supporting multiple xattrs is not currently supported where
   security_old_inode_init_security() was called (mknod, symlink), as it
   requires non-trivial changes that can be done at a later time. Like for
   reiserfs, even if EVM is invoked, it will not provide an xattr (if it is
   not the first to set it, its xattr will be discarded; if it is the first,
   it does not have xattrs to calculate the HMAC on).

   Finally, since security_inode_init_security(), unlike
   security_old_inode_init_security(), returns zero instead of -EOPNOTSUPP if
   no xattrs were provided by LSMs or if inodes are private, additionally
   check in ocfs2_init_security_get() if the xattr name is set.

   If not, act as if security_old_inode_init_security() returned -EOPNOTSUPP,
   and set si->enable to zero to notify to the functions following
   ocfs2_init_security_get() that no xattrs are available.

   Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
   Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
   Acked-by: Joseph Qi <joseph.qi at linux.alibaba.com>
   Reviewed-by: Mimi Zohar <zohar at linux.ibm.com>
   Signed-off-by: Paul Moore <paul at paul-moore.com>

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