md/md-bitmap: fix incorrect usage for sb_index

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: md/md-bitmap: fix incorrect usage for sb_index Commit d7038f951828 ("md-bitmap: don't use ->index for pages backing the bitmap file") removed page->index from bitmap code, but left wrong code logic for clustered-md. current code never set slot offset for cluster nodes, will sometimes cause crash in clustered env. Call trace (partly): md_bitmap_file_set_bit+0x110/0x1d8 [md_mod] md_bitmap_startwrite+0x13c/0x240 [md_mod] raid1_make_request+0x6b0/0x1c08 [raid1] md_handle_request+0x1dc/0x368 [md_mod] md_submit_bio+0x80/0xf8 [md_mod] __submit_bio+0x178/0x300 submit_bio_noacct_nocheck+0x11c/0x338 submit_bio_noacct+0x134/0x614 submit_bio+0x28/0xdc submit_bh_wbc+0x130/0x1cc submit_bh+0x1c/0x28

References

• https://git.kernel.org/stable/c/736ad6c577a367834118f57417038d45bb5e0a31
• https://git.kernel.org/stable/c/55e55eb65fd5e09faf5a0e49ffcdd37905aaf4da
• https://git.kernel.org/stable/c/5a95815b17428ce2f56ec18da5e0d1b2a1a15240
• https://git.kernel.org/stable/c/ecbd8ebb51bf7e4939d83b9e6022a55cac44ef06