From: Hou Tao <houtao1@xxxxxxxxxx> Currently bpf_map_do_batch() first invokes fdget(batch.map_fd) to get the target map file, then it invokes generic_map_update_batch() to do batch update. generic_map_update_batch() will get the target map file by using fdget(batch.map_fd) again and pass it to bpf_map_update_value(). The problem is map file returned by the second fdget() may be NULL or a totally different file compared by map file in bpf_map_do_batch(). The reason is that the first fdget() only guarantees the liveness of struct file instead of file descriptor and the file description may be released by concurrent close() through pick_file(). It doesn't incur any problem as for now, because maps with batch update support don't use map file in .map_fd_get_ptr() ops. But it is better to fix the access of a potentially invalid map file. using __bpf_map_get() again in generic_map_update_batch() can not fix the problem, because batch.map_fd may be closed and reopened, and the returned map file may be different with map file got in bpf_map_do_batch(), so just passing the map file directly to .map_update_batch() in bpf_map_do_batch(). Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx> --- v2: * rewrite the commit message to explain the problem and the reasoning. v1: https://lore.kernel.org/bpf/20221107075537.1445644-1-houtao@xxxxxxxxxxxxxxx include/linux/bpf.h | 5 +++-- kernel/bpf/syscall.c | 31 ++++++++++++++++++------------- 2 files changed, 21 insertions(+), 15 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 798aec816970..20cfe88ee6df 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -85,7 +85,8 @@ struct bpf_map_ops { int (*map_lookup_and_delete_batch)(struct bpf_map *map, const union bpf_attr *attr, union bpf_attr __user *uattr); - int (*map_update_batch)(struct bpf_map *map, const union bpf_attr *attr, + int (*map_update_batch)(struct bpf_map *map, struct file *map_file, + const union bpf_attr *attr, union bpf_attr __user *uattr); int (*map_delete_batch)(struct bpf_map *map, const union bpf_attr *attr, union bpf_attr __user *uattr); @@ -1776,7 +1777,7 @@ void bpf_map_init_from_attr(struct bpf_map *map, union bpf_attr *attr); int generic_map_lookup_batch(struct bpf_map *map, const union bpf_attr *attr, union bpf_attr __user *uattr); -int generic_map_update_batch(struct bpf_map *map, +int generic_map_update_batch(struct bpf_map *map, struct file *map_file, const union bpf_attr *attr, union bpf_attr __user *uattr); int generic_map_delete_batch(struct bpf_map *map, diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 85532d301124..cb8a87277bf8 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -175,8 +175,8 @@ static void maybe_wait_bpf_programs(struct bpf_map *map) synchronize_rcu(); } -static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key, - void *value, __u64 flags) +static int bpf_map_update_value(struct bpf_map *map, struct file *map_file, + void *key, void *value, __u64 flags) { int err; @@ -190,7 +190,7 @@ static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key, map->map_type == BPF_MAP_TYPE_SOCKMAP) { return sock_map_update_elem_sys(map, key, value, flags); } else if (IS_FD_PROG_ARRAY(map)) { - return bpf_fd_array_map_update_elem(map, f.file, key, value, + return bpf_fd_array_map_update_elem(map, map_file, key, value, flags); } @@ -205,12 +205,12 @@ static int bpf_map_update_value(struct bpf_map *map, struct fd f, void *key, flags); } else if (IS_FD_ARRAY(map)) { rcu_read_lock(); - err = bpf_fd_array_map_update_elem(map, f.file, key, value, + err = bpf_fd_array_map_update_elem(map, map_file, key, value, flags); rcu_read_unlock(); } else if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS) { rcu_read_lock(); - err = bpf_fd_htab_map_update_elem(map, f.file, key, value, + err = bpf_fd_htab_map_update_elem(map, map_file, key, value, flags); rcu_read_unlock(); } else if (map->map_type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) { @@ -1390,7 +1390,7 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr) goto free_key; } - err = bpf_map_update_value(map, f, key, value, attr->flags); + err = bpf_map_update_value(map, f.file, key, value, attr->flags); kvfree(value); free_key: @@ -1576,16 +1576,14 @@ int generic_map_delete_batch(struct bpf_map *map, return err; } -int generic_map_update_batch(struct bpf_map *map, +int generic_map_update_batch(struct bpf_map *map, struct file *map_file, const union bpf_attr *attr, union bpf_attr __user *uattr) { void __user *values = u64_to_user_ptr(attr->batch.values); void __user *keys = u64_to_user_ptr(attr->batch.keys); u32 value_size, cp, max_count; - int ufd = attr->batch.map_fd; void *key, *value; - struct fd f; int err = 0; if (attr->batch.elem_flags & ~BPF_F_LOCK) @@ -1612,7 +1610,6 @@ int generic_map_update_batch(struct bpf_map *map, return -ENOMEM; } - f = fdget(ufd); /* bpf_map_do_batch() guarantees ufd is valid */ for (cp = 0; cp < max_count; cp++) { err = -EFAULT; if (copy_from_user(key, keys + cp * map->key_size, @@ -1620,7 +1617,7 @@ int generic_map_update_batch(struct bpf_map *map, copy_from_user(value, values + cp * value_size, value_size)) break; - err = bpf_map_update_value(map, f, key, value, + err = bpf_map_update_value(map, map_file, key, value, attr->batch.elem_flags); if (err) @@ -1633,7 +1630,6 @@ int generic_map_update_batch(struct bpf_map *map, kvfree(value); kvfree(key); - fdput(f); return err; } @@ -4435,6 +4431,15 @@ static int bpf_task_fd_query(const union bpf_attr *attr, err = fn(map, attr, uattr); \ } while (0) +#define BPF_DO_BATCH_WITH_FILE(fn) \ + do { \ + if (!fn) { \ + err = -ENOTSUPP; \ + goto err_put; \ + } \ + err = fn(map, f.file, attr, uattr); \ + } while (0) + static int bpf_map_do_batch(const union bpf_attr *attr, union bpf_attr __user *uattr, int cmd) @@ -4470,7 +4475,7 @@ static int bpf_map_do_batch(const union bpf_attr *attr, else if (cmd == BPF_MAP_LOOKUP_AND_DELETE_BATCH) BPF_DO_BATCH(map->ops->map_lookup_and_delete_batch); else if (cmd == BPF_MAP_UPDATE_BATCH) - BPF_DO_BATCH(map->ops->map_update_batch); + BPF_DO_BATCH_WITH_FILE(map->ops->map_update_batch); else BPF_DO_BATCH(map->ops->map_delete_batch); err_put: -- 2.29.2
