From: zhangyi (F) yi.zhang@huawei.com
[ Upstream commit 7727ae52975d4f4ef7ff69ed8e6e25f6a4168158 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/ext4/block_validity.c | 189 ++++++++++++++++++++++++++++----------- fs/ext4/ext4.h | 10 ++- 2 files changed, 147 insertions(+), 52 deletions(-)
diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c index 8e83741b02e03..d4d4fdfac1a65 100644 --- a/fs/ext4/block_validity.c +++ b/fs/ext4/block_validity.c @@ -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; +err: + release_system_zone(system_blks); + kfree(system_blks); + return ret; }
-/* Called when the filesystem is unmounted */ +/* + * 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_zone *entry, *n; + struct ext4_system_blocks *system_blks;
- rbtree_postorder_for_each_entry_safe(entry, n, - &EXT4_SB(sb)->system_blks, node) - kmem_cache_free(ext4_system_zone_cachep, entry); + 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);
- EXT4_SB(sb)->system_blks = RB_ROOT; + if (system_blks) + call_rcu(&system_blks->rcu, ext4_destroy_system_zone); }
-/* - * 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. - */ 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, diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index bf660aa7a9e08..c025efcbcf27c 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -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 */ @@ -1421,7 +1429,7 @@ 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 */