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ext4: fix potential use after free after remounting with noblock_validity

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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>
This commit is contained in:
zhangyi (F) 2019-08-28 11:13:24 -04:00 committed by Theodore Ts'o
parent 4c273352bb
commit 7727ae5297
2 changed files with 151 additions and 56 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

197
fs/ext4/block_validity.c
View File

@ -38,6 +38,7 @@ int __init ext4_init_system_zone(void)
void ext4_exit_system_zone(void)
{
rcu_barrier();
kmem_cache_destroy(ext4_system_zone_cachep);
}
@ -49,17 +50,26 @@ static inline int can_merge(struct ext4_system_zone *entry1,
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_sb_info *sbi,
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 = &sbi->system_blks.rb_node, *node;
struct rb_node **n = &system_blks->root.rb_node, *node;
struct rb_node *parent = NULL, *new_node = NULL;
while (*n) {
@ -91,7 +101,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
new_node = &new_entry->node;
rb_link_node(new_node, parent, n);
rb_insert_color(new_node, &sbi->system_blks);
rb_insert_color(new_node, &system_blks->root);
}
/* Can we merge to the left? */
@ -101,7 +111,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
if (can_merge(entry, new_entry)) {
new_entry->start_blk = entry->start_blk;
new_entry->count += entry->count;
rb_erase(node, &sbi->system_blks);
rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
@ -112,7 +122,7 @@ static int add_system_zone(struct ext4_sb_info *sbi,
entry = rb_entry(node, struct ext4_system_zone, node);
if (can_merge(new_entry, entry)) {
new_entry->count += entry->count;
rb_erase(node, &sbi->system_blks);
rb_erase(node, &system_blks->root);
kmem_cache_free(ext4_system_zone_cachep, entry);
}
}
@ -126,7 +136,7 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
int first = 1;
printk(KERN_INFO "System zones: ");
node = rb_first(&sbi->system_blks);
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 ? "" : ", ",
@ -137,7 +147,47 @@ static void debug_print_tree(struct ext4_sb_info *sbi)
printk(KERN_CONT "\n");
}
static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
/*
* 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);
@ -163,14 +213,15 @@ static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
if (n == 0) {
i++;
} else {
if (!ext4_data_block_valid(sbi, map.m_pblk, n)) {
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(sbi, map.m_pblk, n);
err = add_system_zone(system_blks, map.m_pblk, n);
if (err < 0)
break;
i += n;
@ -180,94 +231,130 @@ static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
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.rb_node)
if (sbi->system_blks)
ext4_release_system_zone(sb);
return 0;
}
if (sbi->system_blks.rb_node)
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(sbi, ext4_group_first_block_no(sb, i),
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(sbi, ext4_block_bitmap(sb, gdp), 1);
ret = add_system_zone(system_blks,
ext4_block_bitmap(sb, gdp), 1);
if (ret)
return ret;
ret = add_system_zone(sbi, ext4_inode_bitmap(sb, gdp), 1);
goto err;
ret = add_system_zone(system_blks,
ext4_inode_bitmap(sb, gdp), 1);
if (ret)
return ret;
ret = add_system_zone(sbi, ext4_inode_table(sb, gdp),
goto err;
ret = add_system_zone(system_blks,
ext4_inode_table(sb, gdp),
sbi->s_itb_per_group);
if (ret)
return ret;
goto err;
}
if (ext4_has_feature_journal(sb) && sbi->s_es->s_journal_inum) {
ret = ext4_protect_reserved_inode(sb,
ret = ext4_protect_reserved_inode(sb, system_blks,
le32_to_cpu(sbi->s_es->s_journal_inum));
if (ret)
return 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;
}
/* Called when the filesystem is unmounted */
void ext4_release_system_zone(struct super_block *sb)
{
struct ext4_system_zone *entry, *n;
rbtree_postorder_for_each_entry_safe(entry, n,
&EXT4_SB(sb)->system_blks, node)
kmem_cache_free(ext4_system_zone_cachep, entry);
EXT4_SB(sb)->system_blks = RB_ROOT;
err:
release_system_zone(system_blks);
kfree(system_blks);
return ret;
}
/*
* 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.
* 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_zone *entry;
struct rb_node *n = sbi->system_blks.rb_node;
struct ext4_system_blocks *system_blks;
int ret;
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;
}
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;
/*
* 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,

10
fs/ext4/ext4.h
View File

@ -184,6 +184,14 @@ struct ext4_map_blocks {
unsigned int m_flags;
};
/*
* Block validity checking, system zone rbtree.
*/
struct ext4_system_blocks {
struct rb_root root;
struct rcu_head rcu;
};
/*
* Flags for ext4_io_end->flags
*/
@ -1431,7 +1439,7 @@ struct ext4_sb_info {
int s_jquota_fmt; /* Format of quota to use */
#endif
unsigned int s_want_extra_isize; /* New inodes should reserve # bytes */
struct rb_root system_blks;
struct ext4_system_blocks __rcu *system_blks;
#ifdef EXTENTS_STATS
/* ext4 extents stats */