mke2fs -G option allows root user to set flex_bg count (power of 2).
However ext4 has bad metadata layout if we specify more than or equal to
2^32 to mke2fs -G, because of the 32bit shift operation
in ext2fs_allocate_group_table().
And the maximum block group count of ext4 is 2^32 -1 (ext4_group_t s_groups_count),
so diallow more than 2^32 flex_bg count.
Steps to reproduce:
# mke2fs -t ext4 -G 4294967296 DEV
# dumpe2fs DEV
<snip>
Flex block group size: 1 <----- flex_bg is 1!
<snip>
Group 0: (Blocks 0-32767)
Checksum 0x4afd, unused inodes 7541
Primary superblock at 0, Group descriptors at 1-1
Reserved GDT blocks at 2-59
Block bitmap at 60 (+60), Inode bitmap at 61 (+61)
Inode table at 62-533 (+62)
32228 free blocks, 7541 free inodes, 2 directories, 7541 unused inodes
Free blocks: 540-32767
Free inodes: 12-7552
Group 1: (Blocks 32768-65535) [INODE_UNINIT]
Checksum 0xc890, unused inodes 7552
Backup superblock at 32768, Group descriptors at 32769-32769
Reserved GDT blocks at 32770-32827
Block bitmap at 32828 (+60), Inode bitmap at 32829 (+61)
Inode table at 32830-33301 (+62)
32234 free blocks, 7552 free inodes, 0 directories, 7552 unused inodes
Free blocks: 33302-65535
Free inodes: 7553-15104
<snip>
Signed-off-by: Akira Fujita <a-fujita@xxxxxxxxxxxxx>
---
misc/mke2fs.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index b451cc3..b9145d1 100644
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -1605,6 +1605,12 @@ profile_error:
_("flex_bg size must be a power of 2"));
exit(1);
}
+ if (flex_bg_size > MAX_32_NUM) {
+ com_err(program_name, 0,
+ _("flex_bg size (%lu) must be less than"
+ " or equal to 2^31"), flex_bg_size);
+ exit(1);
+ }
break;
case 'i':
inode_ratio = strtoul(optarg, &tmp, 0);
--
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