shmem: use ramfs_kill_sb() for kill_sb method of ramfs-based tmpfs

CVE-2023-53391

What is CVE-2023-53391?

In the Linux kernel, the following vulnerability has been resolved:

shmem: use ramfs_kill_sb() for kill_sb method of ramfs-based tmpfs

As the ramfs-based tmpfs uses ramfs_init_fs_context() for the init_fs_context method, which allocates fc->s_fs_info, use ramfs_kill_sb() to free it and avoid a memory leak.

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