PC-BSD/trueos ec03032sys/fs/ext2fs ext2_vfsops.c ext2_alloc.c

MFC r344751:
Make superblock reading logic more strict.

Add more on-disk superblock consistency checks to ext2_compute_sb_data() function.
It should decrease the probability of mounting filesystems with corrupted superblock data.

Reviewed by:    pfg

Differential Revision:    https://reviews.freebsd.org/D19322
DeltaFile
+207-59sys/fs/ext2fs/ext2_vfsops.c
+5-5sys/fs/ext2fs/ext2_alloc.c
+3-2sys/fs/ext2fs/ext2fs.h
+3-0sys/fs/ext2fs/ext2_extern.h
+218-664 files

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