[PATCH 03/46] mm/memfd: check for real shmem inodes before accessing shmem state

[sashiko-bot at kernel.org]

> shmem_file() only checks a file's backing mapping. That mapping can belong
> to another file, as with a Coda file backed by a tmpfs container after
> mmap(). It does not establish that file_inode(file) is a shmem inode.
> 
> Seal handling and memfd preservation use this check before accessing
> shmem inode state, so they can access an inode of the wrong type.
> 
> Add file_inode_is_shmem() to check the inode's file operations in both
> paths. This identifies regular shmem inodes, including those used by
> memfds and ordinary tmpfs files, independently of wrapper file operations.
> 
> Fixes: c49fcfcda8b5 ("mm/shmem: update file sealing comments and file checking")
> Fixes: b3749f174d68 ("mm: memfd_luo: allow preserving memfd")
> Cc: stable at vger.kernel.org
> Reported-by: Chris Mason <mason at kernel.org>
> Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org?part=3