Commit 8ebe667c authored Jan 22, 2015 by Alexei Starovoitov Committed by David S. Miller Jan 26, 2015

bpf: rcu lock must not be held when calling copy_to_user()



BUG: sleeping function called from invalid context at mm/memory.c:3732
in_atomic(): 0, irqs_disabled(): 0, pid: 671, name: test_maps
1 lock held by test_maps/671:
 #0:  (rcu_read_lock){......}, at: [<0000000000264190>] map_lookup_elem+0xe8/0x260
Call Trace:
([<0000000000115b7e>] show_trace+0x12e/0x150)
 [<0000000000115c40>] show_stack+0xa0/0x100
 [<00000000009b163c>] dump_stack+0x74/0xc8
 [<000000000017424a>] ___might_sleep+0x23a/0x248
 [<00000000002b58e8>] might_fault+0x70/0xe8
 [<0000000000264230>] map_lookup_elem+0x188/0x260
 [<0000000000264716>] SyS_bpf+0x20e/0x840

Fix it by allocating temporary buffer to store map element value.

Fixes: db20fd2b ("bpf: add lookup/update/delete/iterate methods to BPF maps")
Reported-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 600ddd68

kernel/bpf/syscall.c

+17 −8

Original line number	Diff line number	Diff line
		@@ -150,7 +150,7 @@ static int map_lookup_elem(union bpf_attr *attr)
		int ufd = attr->map_fd;
		struct fd f = fdget(ufd);
		struct bpf_map *map;
		void key, value;
		void key, value, *ptr;
		int err;

		if (CHECK_ATTR(BPF_MAP_LOOKUP_ELEM))
		@@ -169,20 +169,29 @@ static int map_lookup_elem(union bpf_attr *attr)
		if (copy_from_user(key, ukey, map->key_size) != 0)
		goto free_key;

		err = -ENOENT;
		rcu_read_lock();
		value = map->ops->map_lookup_elem(map, key);
		err = -ENOMEM;
		value = kmalloc(map->value_size, GFP_USER);
		if (!value)
		goto err_unlock;
		goto free_key;

		rcu_read_lock();
		ptr = map->ops->map_lookup_elem(map, key);
		if (ptr)
		memcpy(value, ptr, map->value_size);
		rcu_read_unlock();

		err = -ENOENT;
		if (!ptr)
		goto free_value;

		err = -EFAULT;
		if (copy_to_user(uvalue, value, map->value_size) != 0)
		goto err_unlock;
		goto free_value;

		err = 0;

		err_unlock:
		rcu_read_unlock();
		free_value:
		kfree(value);
		free_key:
		kfree(key);
		err_put:

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