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Correctly calculate tot_used_blocks on ext4 with uninit_bg

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The calculated number of blocks to encrypt is too high on ext4
filesystems that have the uninit_bg feature.  This is because the
calculation assumes that all blocks not counted in bg_free_blocks_count
need to encrypted.  But actually, uninitialized block groups have inode
blocks which vold doesn't encrypt since they are uninitialized, but they
are "allocated" and thus reduce bg_free_blocks_count.

Therefore, add a helper function num_base_meta_blocks_in_group() which
returns the number of blocks to encrypt in an uninitialized block group.
Use it both for the encryption and for calculating 'tot_used_blocks'.

Also compute 'tot_used_blocks' additively rather than subtractively, as
this is easier to understand.

Test: see I08fc8465f7962abd698904b5466f3ed080d53953
Change-Id: I4d2cb40291da67dd1bafd61289ccb9e6343bfda3
This commit is contained in:
Eric Biggers 2020-11-03 14:11:01 -08:00
parent b3ba087d9c
commit 7e70d6939d
1 changed files with 27 additions and 11 deletions
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38
EncryptInplace.cpp
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@ -155,6 +155,22 @@ static int flush_outstanding_data(struct encryptGroupsData* data) {
return 0;
}
static uint64_t first_block_in_group(uint32_t group) {
return aux_info.first_data_block + (group * (uint64_t)info.blocks_per_group);
}
static uint32_t num_blocks_in_group(uint32_t group) {
uint64_t remaining = aux_info.len_blocks - first_block_in_group(group);
return std::min<uint64_t>(info.blocks_per_group, remaining);
}
// In block groups with an uninitialized block bitmap, we only need to encrypt
// the backup superblock and the block group descriptors (if they are present).
static uint32_t num_base_meta_blocks_in_group(uint64_t group) {
if (!ext4_bg_has_super_block(group)) return 0;
return 1 + aux_info.bg_desc_blocks;
}
static int encrypt_groups(struct encryptGroupsData* data) {
unsigned int i;
u8* block_bitmap = 0;
@ -177,8 +193,7 @@ static int encrypt_groups(struct encryptGroupsData* data) {
for (i = 0; i < aux_info.groups; ++i) {
LOG(INFO) << "Encrypting group " << i;
u32 first_block = aux_info.first_data_block + i * info.blocks_per_group;
u32 block_count = std::min(info.blocks_per_group, (u32)(aux_info.len_blocks - first_block));
u32 block_count = num_blocks_in_group(i);
off64_t offset = (u64)info.block_size * aux_info.bg_desc[i].bg_block_bitmap;
@ -188,20 +203,17 @@ static int encrypt_groups(struct encryptGroupsData* data) {
goto errout;
}
offset = (u64)info.block_size * first_block;
offset = (u64)info.block_size * first_block_in_group(i);
data->count = 0;
for (block = 0; block < block_count; block++) {
int used;
if (aux_info.bg_desc[i].bg_flags & EXT4_BG_BLOCK_UNINIT) {
// In block groups with an uninitialized block bitmap, we only
// need to encrypt the backup superblock (if one is present).
used = (ext4_bg_has_super_block(i) && block < 1 + aux_info.bg_desc_blocks);
} else {
if (aux_info.bg_desc[i].bg_flags & EXT4_BG_BLOCK_UNINIT)
used = (block < num_base_meta_blocks_in_group(i));
else
used = bitmap_get_bit(block_bitmap, block);
}
update_progress(data, used);
if (used) {
@ -282,9 +294,13 @@ static int cryptfs_enable_inplace_ext4(const char* crypto_blkdev, const char* re
LOG(INFO) << "Encrypting ext4 filesystem in place...";
data.tot_used_blocks = size / CRYPT_SECTORS_PER_BUFSIZE;
data.tot_used_blocks = 0;
for (i = 0; i < aux_info.groups; ++i) {
data.tot_used_blocks -= aux_info.bg_desc[i].bg_free_blocks_count;
if (aux_info.bg_desc[i].bg_flags & EXT4_BG_BLOCK_UNINIT)
data.tot_used_blocks += num_base_meta_blocks_in_group(i);
else
data.tot_used_blocks +=
(num_blocks_in_group(i) - aux_info.bg_desc[i].bg_free_blocks_count);
}
data.one_pct = data.tot_used_blocks / 100;