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pstore: inode: Only d_invalidate() is needed

Steve Best requested to merge sfbest/centos-stream-9:35207 into main

JIRA: https://issues.redhat.com/browse/RHEL-35207
CVE: CVE-2024-27389

Build Info: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=61085296

Tested: Did sanity pstore testing using Intel (intel-eaglestream-emr-01) system.

commit a43e0fc5e9134a46515de2f2f8d4100b74e50de3
Author: Kees Cook keescook@chromium.org
Date: Thu Feb 22 09:48:46 2024 -0800

pstore: inode: Only d_invalidate() is needed  

Unloading a modular pstore backend with records in pstorefs would  
trigger the dput() double-drop warning:  

  WARNING: CPU: 0 PID: 2569 at fs/dcache.c:762 dput.part.0+0x3f3/0x410  

Using the combo of d_drop()/dput() (as mentioned in  
Documentation/filesystems/vfs.rst) isn't the right approach here, and  
leads to the reference counting problem seen above. Use d_invalidate()  
and update the code to not bother checking for error codes that can  
never happen.  

Suggested-by: Alexander Viro <viro@zeniv.linux.org.uk>  
Fixes: 609e28bb139e ("pstore: Remove filesystem records when backend is unregistered")  
Signed-off-by: Kees Cook <keescook@chromium.org>  
---  
Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com>  
Cc: Tony Luck <tony.luck@intel.com>  
Cc: linux-hardening@vger.kernel.org

Signed-off-by: Steve Best sbest@redhat.com

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