ext4: make sure bitmaps and the inode table don't overlap with bg descriptors

commit 77260807d1170a8cf35dbb06e07461a655f67eee upstream.

It's really bad when the allocation bitmaps and the inode table
overlap with the block group descriptors, since it causes random
corruption of the bg descriptors.  So we really want to head those off
at the pass.

https://bugzilla.kernel.org/show_bug.cgi?id=199865

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: Open-code sb_rdonly()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d15b7d6c67a3e10ad324a49f51972b008c865160..7c7bb3b18624cbd6cf123d1a420dacb550235393 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2086,6 +2086,7 @@ static int ext4_check_descriptors(struct super_block *sb,
        struct ext4_sb_info *sbi = EXT4_SB(sb);
        ext4_fsblk_t first_block = le32_to_cpu(sbi->s_es->s_first_data_block);
        ext4_fsblk_t last_block;
+       ext4_fsblk_t last_bg_block = sb_block + ext4_bg_num_gdb(sb, 0) + 1;
        ext4_fsblk_t block_bitmap;
        ext4_fsblk_t inode_bitmap;
        ext4_fsblk_t inode_table;
@@ -2118,6 +2119,14 @@ static int ext4_check_descriptors(struct super_block *sb,
                        if (!(sb->s_flags & MS_RDONLY))
                                return 0;
                }
+               if (block_bitmap >= sb_block + 1 &&
+                   block_bitmap <= last_bg_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Block bitmap for group %u overlaps "
+                                "block group descriptors", i);
+                       if (!(sb->s_flags & MS_RDONLY))
+                               return 0;
+               }
                if (block_bitmap < first_block || block_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Block bitmap for group %u not in group "
@@ -2132,6 +2141,14 @@ static int ext4_check_descriptors(struct super_block *sb,
                        if (!(sb->s_flags & MS_RDONLY))
                                return 0;
                }
+               if (inode_bitmap >= sb_block + 1 &&
+                   inode_bitmap <= last_bg_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Inode bitmap for group %u overlaps "
+                                "block group descriptors", i);
+                       if (!(sb->s_flags & MS_RDONLY))
+                               return 0;
+               }
                if (inode_bitmap < first_block || inode_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Inode bitmap for group %u not in group "
@@ -2146,6 +2163,14 @@ static int ext4_check_descriptors(struct super_block *sb,
                        if (!(sb->s_flags & MS_RDONLY))
                                return 0;
                }
+               if (inode_table >= sb_block + 1 &&
+                   inode_table <= last_bg_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Inode table for group %u overlaps "
+                                "block group descriptors", i);
+                       if (!(sb->s_flags & MS_RDONLY))
+                               return 0;
+               }
                if (inode_table < first_block ||
                    inode_table + sbi->s_itb_per_group - 1 > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "