ext4: filter out EXT4_FC_REPLAY from on-disk superblock field s_state

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ext4: filter out EXT4_FC_REPLAY from on-disk superblock field s_state The EXT4_FC_REPLAY bit in sbi->s_mount_state is used to indicate that we are in the middle of replay the fast commit journal. This was actually a mistake, since the sbi->s_mount_info is initialized from es->s_state. Arguably s_mount_state is misleadingly named, but the name is historical --- s_mount_state and s_state dates back to ext2. What should have been used is the ext4_{set,clear,test}_mount_flag() inline functions, which sets EXT4_MF_* bits in sbi->s_mount_flags. The problem with using EXT4_FC_REPLAY is that a maliciously corrupted superblock could result in EXT4_FC_REPLAY getting set in s_mount_state. This bypasses some sanity checks, and this can trigger a BUG() in ext4_es_cache_extent(). As a easy-to-backport-fix, filter out the EXT4_FC_REPLAY bit for now. We should eventually transition away from EXT4_FC_REPLAY to something like EXT4_MF_REPLAY.

References

• https://git.kernel.org/stable/c/cc5b09cb6dacd4b32640537929ab4ee8fb2b9e04
• https://git.kernel.org/stable/c/b99fd73418350dea360da8311e87a6a7b0e15a4c
• https://git.kernel.org/stable/c/af2f1932743fb52ebcb008ad7ac500d9df0aa796
• https://git.kernel.org/stable/c/55b4dbb29054a05d839562f6d635ce05669b016d
• https://git.kernel.org/stable/c/c878bea3c9d724ddfa05a813f30de3d25a0ba83f