linux/fs/ext4/block_validity.c
zhangyi (F) 7727ae5297 ext4: fix potential use after free after remounting with noblock_validity
Remount process will release system zone which was allocated before if
"noblock_validity" is specified. If we mount an ext4 file system to two
mountpoints with default mount options, and then remount one of them
with "noblock_validity", it may trigger a use after free problem when
someone accessing the other one.

 # mount /dev/sda foo
 # mount /dev/sda bar

User access mountpoint "foo"   |   Remount mountpoint "bar"
                               |
ext4_map_blocks()              |   ext4_remount()
check_block_validity()         |   ext4_setup_system_zone()
ext4_data_block_valid()        |   ext4_release_system_zone()
                               |   free system_blks rb nodes
access system_blks rb nodes    |
trigger use after free         |

This problem can also be reproduced by one mountpint, At the same time,
add_system_zone() can get called during remount as well so there can be
racing ext4_data_block_valid() reading the rbtree at the same time.

This patch add RCU to protect system zone from releasing or building
when doing a remount which inverse current "noblock_validity" mount
option. It assign the rbtree after the whole tree was complete and
do actual freeing after rcu grace period, avoid any intermediate state.

Reported-by: syzbot+1e470567330b7ad711d5@syzkaller.appspotmail.com
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
2019-08-28 11:13:24 -04:00

386 lines
9.9 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* linux/fs/ext4/block_validity.c
*
* Copyright (C) 2009
* Theodore Ts'o (tytso@mit.edu)
*
* Track which blocks in the filesystem are metadata blocks that
* should never be used as data blocks by files or directories.
*/
#include <linux/time.h>
#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/quotaops.h>
#include <linux/buffer_head.h>
#include <linux/swap.h>
#include <linux/pagemap.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include "ext4.h"
struct ext4_system_zone {
struct rb_node node;
ext4_fsblk_t start_blk;
unsigned int count;
};
static struct kmem_cache *ext4_system_zone_cachep;
int __init ext4_init_system_zone(void)
{
ext4_system_zone_cachep = KMEM_CACHE(ext4_system_zone, 0);
if (ext4_system_zone_cachep == NULL)
return -ENOMEM;
return 0;
}
void ext4_exit_system_zone(void)
{
rcu_barrier();
kmem_cache_destroy(ext4_system_zone_cachep);
}
static inline int can_merge(struct ext4_system_zone *entry1,
struct ext4_system_zone *entry2)
{
if ((entry1->start_blk + entry1->count) == entry2->start_blk)
return 1;
return 0;
}
static void release_system_zone(struct ext4_system_blocks *system_blks)
{
struct ext4_system_zone *entry, *n;
rbtree_postorder_for_each_entry_safe(entry, n,
&system_blks->root, node)
kmem_cache_free(ext4_system_zone_cachep, entry);
}
/*
* Mark a range of blocks as belonging to the "system zone" --- that
* is, filesystem metadata blocks which should never be used by
* inodes.
*/
static int add_system_zone(struct ext4_system_blocks *system_blks,
ext4_fsblk_t start_blk,
unsigned int count)
{
struct ext4_system_zone *new_entry = NULL, *entry;
struct rb_node **n = &system_blks->root.rb_node, *node;
struct rb_node *parent = NULL, *new_node = NULL;
while (*n) {
parent = *n;
entry = rb_entry(parent, struct ext4_system_zone, node);
if (start_blk < entry->start_blk)
n = &(*n)->rb_left;
else if (start_blk >= (entry->start_blk + entry->count))
n = &(*n)->rb_right;
else {
if (start_blk + count > (entry->start_blk +
entry->count))
entry->count = (start_blk + count -
entry->start_blk);
new_node = *n;
new_entry = rb_entry(new_node, struct ext4_system_zone,
node);
break;
}
}
if (!new_entry) {
new_entry = kmem_cache_alloc(ext4_system_zone_cachep,
GFP_KERNEL);
if (!new_entry)
return -ENOMEM;
new_entry->start_blk = start_blk;
new_entry->count = count;
new_node = &new_entry->node;
rb_link_node(new_node, parent, n);
rb_insert_color(new_node, &system_blks->root);
}
/* Can we merge to the left? */
node = rb_prev(new_node);
if (node) {
entry = rb_entry(node, struct ext4_system_zone, node);
if (can_merge(entry, new_entry)) {
new_entry->start_blk = entry->start_blk;
new_entry->count += entry->count;
rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
/* Can we merge to the right? */
node = rb_next(new_node);
if (node) {
entry = rb_entry(node, struct ext4_system_zone, node);
if (can_merge(new_entry, entry)) {
new_entry->count += entry->count;
rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
return 0;
}
static void debug_print_tree(struct ext4_sb_info *sbi)
{
struct rb_node *node;
struct ext4_system_zone *entry;
int first = 1;
printk(KERN_INFO "System zones: ");
node = rb_first(&sbi->system_blks->root);
while (node) {
entry = rb_entry(node, struct ext4_system_zone, node);
printk(KERN_CONT "%s%llu-%llu", first ? "" : ", ",
entry->start_blk, entry->start_blk + entry->count - 1);
first = 0;
node = rb_next(node);
}
printk(KERN_CONT "\n");
}
/*
* Returns 1 if the passed-in block region (start_blk,
* start_blk+count) is valid; 0 if some part of the block region
* overlaps with filesystem metadata blocks.
*/
static int ext4_data_block_valid_rcu(struct ext4_sb_info *sbi,
struct ext4_system_blocks *system_blks,
ext4_fsblk_t start_blk,
unsigned int count)
{
struct ext4_system_zone *entry;
struct rb_node *n;
if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
(start_blk + count < start_blk) ||
(start_blk + count > ext4_blocks_count(sbi->s_es))) {
sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
return 0;
}
if (system_blks == NULL)
return 1;
n = system_blks->root.rb_node;
while (n) {
entry = rb_entry(n, struct ext4_system_zone, node);
if (start_blk + count - 1 < entry->start_blk)
n = n->rb_left;
else if (start_blk >= (entry->start_blk + entry->count))
n = n->rb_right;
else {
sbi->s_es->s_last_error_block = cpu_to_le64(start_blk);
return 0;
}
}
return 1;
}
static int ext4_protect_reserved_inode(struct super_block *sb,
struct ext4_system_blocks *system_blks,
u32 ino)
{
struct inode *inode;
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_map_blocks map;
u32 i = 0, num;
int err = 0, n;
if ((ino < EXT4_ROOT_INO) ||
(ino > le32_to_cpu(sbi->s_es->s_inodes_count)))
return -EINVAL;
inode = ext4_iget(sb, ino, EXT4_IGET_SPECIAL);
if (IS_ERR(inode))
return PTR_ERR(inode);
num = (inode->i_size + sb->s_blocksize - 1) >> sb->s_blocksize_bits;
while (i < num) {
map.m_lblk = i;
map.m_len = num - i;
n = ext4_map_blocks(NULL, inode, &map, 0);
if (n < 0) {
err = n;
break;
}
if (n == 0) {
i++;
} else {
if (!ext4_data_block_valid_rcu(sbi, system_blks,
map.m_pblk, n)) {
ext4_error(sb, "blocks %llu-%llu from inode %u "
"overlap system zone", map.m_pblk,
map.m_pblk + map.m_len - 1, ino);
err = -EFSCORRUPTED;
break;
}
err = add_system_zone(system_blks, map.m_pblk, n);
if (err < 0)
break;
i += n;
}
}
iput(inode);
return err;
}
static void ext4_destroy_system_zone(struct rcu_head *rcu)
{
struct ext4_system_blocks *system_blks;
system_blks = container_of(rcu, struct ext4_system_blocks, rcu);
release_system_zone(system_blks);
kfree(system_blks);
}
/*
* Build system zone rbtree which is used for block validity checking.
*
* The update of system_blks pointer in this function is protected by
* sb->s_umount semaphore. However we have to be careful as we can be
* racing with ext4_data_block_valid() calls reading system_blks rbtree
* protected only by RCU. That's why we first build the rbtree and then
* swap it in place.
*/
int ext4_setup_system_zone(struct super_block *sb)
{
ext4_group_t ngroups = ext4_get_groups_count(sb);
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_system_blocks *system_blks;
struct ext4_group_desc *gdp;
ext4_group_t i;
int flex_size = ext4_flex_bg_size(sbi);
int ret;
if (!test_opt(sb, BLOCK_VALIDITY)) {
if (sbi->system_blks)
ext4_release_system_zone(sb);
return 0;
}
if (sbi->system_blks)
return 0;
system_blks = kzalloc(sizeof(*system_blks), GFP_KERNEL);
if (!system_blks)
return -ENOMEM;
for (i=0; i < ngroups; i++) {
cond_resched();
if (ext4_bg_has_super(sb, i) &&
((i < 5) || ((i % flex_size) == 0)))
add_system_zone(system_blks,
ext4_group_first_block_no(sb, i),
ext4_bg_num_gdb(sb, i) + 1);
gdp = ext4_get_group_desc(sb, i, NULL);
ret = add_system_zone(system_blks,
ext4_block_bitmap(sb, gdp), 1);
if (ret)
goto err;
ret = add_system_zone(system_blks,
ext4_inode_bitmap(sb, gdp), 1);
if (ret)
goto err;
ret = add_system_zone(system_blks,
ext4_inode_table(sb, gdp),
sbi->s_itb_per_group);
if (ret)
goto err;
}
if (ext4_has_feature_journal(sb) && sbi->s_es->s_journal_inum) {
ret = ext4_protect_reserved_inode(sb, system_blks,
le32_to_cpu(sbi->s_es->s_journal_inum));
if (ret)
goto err;
}
/*
* System blks rbtree complete, announce it once to prevent racing
* with ext4_data_block_valid() accessing the rbtree at the same
* time.
*/
rcu_assign_pointer(sbi->system_blks, system_blks);
if (test_opt(sb, DEBUG))
debug_print_tree(sbi);
return 0;
err:
release_system_zone(system_blks);
kfree(system_blks);
return ret;
}
/*
* Called when the filesystem is unmounted or when remounting it with
* noblock_validity specified.
*
* The update of system_blks pointer in this function is protected by
* sb->s_umount semaphore. However we have to be careful as we can be
* racing with ext4_data_block_valid() calls reading system_blks rbtree
* protected only by RCU. So we first clear the system_blks pointer and
* then free the rbtree only after RCU grace period expires.
*/
void ext4_release_system_zone(struct super_block *sb)
{
struct ext4_system_blocks *system_blks;
system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks,
lockdep_is_held(&sb->s_umount));
rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL);
if (system_blks)
call_rcu(&system_blks->rcu, ext4_destroy_system_zone);
}
int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk,
unsigned int count)
{
struct ext4_system_blocks *system_blks;
int ret;
/*
* Lock the system zone to prevent it being released concurrently
* when doing a remount which inverse current "[no]block_validity"
* mount option.
*/
rcu_read_lock();
system_blks = rcu_dereference(sbi->system_blks);
ret = ext4_data_block_valid_rcu(sbi, system_blks, start_blk,
count);
rcu_read_unlock();
return ret;
}
int ext4_check_blockref(const char *function, unsigned int line,
struct inode *inode, __le32 *p, unsigned int max)
{
struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es;
__le32 *bref = p;
unsigned int blk;
if (ext4_has_feature_journal(inode->i_sb) &&
(inode->i_ino ==
le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_journal_inum)))
return 0;
while (bref < p+max) {
blk = le32_to_cpu(*bref++);
if (blk &&
unlikely(!ext4_data_block_valid(EXT4_SB(inode->i_sb),
blk, 1))) {
es->s_last_error_block = cpu_to_le64(blk);
ext4_error_inode(inode, function, line, blk,
"invalid block");
return -EFSCORRUPTED;
}
}
return 0;
}