From: Filipe Manana Date: Thu, 26 Feb 2026 23:41:07 +0000 (+0000) Subject: btrfs: fix transaction abort on set received ioctl due to item overflow X-Git-Tag: v7.0-rc4~36^2~3 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=87f2c46003fce4d739138aab4af1942b1afdadac;p=thirdparty%2Fkernel%2Fstable.git btrfs: fix transaction abort on set received ioctl due to item overflow If the set received ioctl fails due to an item overflow when attempting to add the BTRFS_UUID_KEY_RECEIVED_SUBVOL we have to abort the transaction since we did some metadata updates before. This means that if a user calls this ioctl with the same received UUID field for a lot of subvolumes, we will hit the overflow, trigger the transaction abort and turn the filesystem into RO mode. A malicious user could exploit this, and this ioctl does not even requires that a user has admin privileges (CAP_SYS_ADMIN), only that he/she owns the subvolume. Fix this by doing an early check for item overflow before starting a transaction. This is also race safe because we are holding the subvol_sem semaphore in exclusive (write) mode. A test case for fstests will follow soon. Fixes: dd5f9615fc5c ("Btrfs: maintain subvolume items in the UUID tree") CC: stable@vger.kernel.org # 3.12+ Reviewed-by: Anand Jain Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba --- diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 1d22c5c05b50e..56d17eedaf903 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -3929,6 +3929,25 @@ static long _btrfs_ioctl_set_received_subvol(struct file *file, goto out; } + received_uuid_changed = memcmp(root_item->received_uuid, sa->uuid, + BTRFS_UUID_SIZE); + + /* + * Before we attempt to add the new received uuid, check if we have room + * for it in case there's already an item. If the size of the existing + * item plus this root's ID (u64) exceeds the maximum item size, we can + * return here without the need to abort a transaction. If we don't do + * this check, the btrfs_uuid_tree_add() call below would fail with + * -EOVERFLOW and result in a transaction abort. Malicious users could + * exploit this to turn the fs into RO mode. + */ + if (received_uuid_changed && !btrfs_is_empty_uuid(sa->uuid)) { + ret = btrfs_uuid_tree_check_overflow(fs_info, sa->uuid, + BTRFS_UUID_KEY_RECEIVED_SUBVOL); + if (ret < 0) + goto out; + } + /* * 1 - root item * 2 - uuid items (received uuid + subvol uuid) @@ -3944,8 +3963,6 @@ static long _btrfs_ioctl_set_received_subvol(struct file *file, sa->rtime.sec = ct.tv_sec; sa->rtime.nsec = ct.tv_nsec; - received_uuid_changed = memcmp(root_item->received_uuid, sa->uuid, - BTRFS_UUID_SIZE); if (received_uuid_changed && !btrfs_is_empty_uuid(root_item->received_uuid)) { ret = btrfs_uuid_tree_remove(trans, root_item->received_uuid, diff --git a/fs/btrfs/uuid-tree.c b/fs/btrfs/uuid-tree.c index f24c14b9bb2fd..43c17a1d34513 100644 --- a/fs/btrfs/uuid-tree.c +++ b/fs/btrfs/uuid-tree.c @@ -199,6 +199,44 @@ int btrfs_uuid_tree_remove(struct btrfs_trans_handle *trans, const u8 *uuid, u8 return 0; } +/* + * Check if we can add one root ID to a UUID key. + * If the key does not yet exists, we can, otherwise only if extended item does + * not exceeds the maximum item size permitted by the leaf size. + * + * Returns 0 on success, negative value on error. + */ +int btrfs_uuid_tree_check_overflow(struct btrfs_fs_info *fs_info, + const u8 *uuid, u8 type) +{ + BTRFS_PATH_AUTO_FREE(path); + int ret; + u32 item_size; + struct btrfs_key key; + + if (WARN_ON_ONCE(!fs_info->uuid_root)) + return -EINVAL; + + path = btrfs_alloc_path(); + if (!path) + return -ENOMEM; + + btrfs_uuid_to_key(uuid, type, &key); + ret = btrfs_search_slot(NULL, fs_info->uuid_root, &key, path, 0, 0); + if (ret < 0) + return ret; + if (ret > 0) + return 0; + + item_size = btrfs_item_size(path->nodes[0], path->slots[0]); + + if (sizeof(struct btrfs_item) + item_size + sizeof(u64) > + BTRFS_LEAF_DATA_SIZE(fs_info)) + return -EOVERFLOW; + + return 0; +} + static int btrfs_uuid_iter_rem(struct btrfs_root *uuid_root, u8 *uuid, u8 type, u64 subid) { diff --git a/fs/btrfs/uuid-tree.h b/fs/btrfs/uuid-tree.h index c60ad20325cce..02b235a3653f0 100644 --- a/fs/btrfs/uuid-tree.h +++ b/fs/btrfs/uuid-tree.h @@ -12,6 +12,8 @@ int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, const u8 *uuid, u8 typ u64 subid); int btrfs_uuid_tree_remove(struct btrfs_trans_handle *trans, const u8 *uuid, u8 type, u64 subid); +int btrfs_uuid_tree_check_overflow(struct btrfs_fs_info *fs_info, + const u8 *uuid, u8 type); int btrfs_uuid_tree_iterate(struct btrfs_fs_info *fs_info); int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info); int btrfs_uuid_scan_kthread(void *data);