Commit abf2e7d6 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller

bpf: add missing rcu protection when releasing programs from prog_array

Normally the program attachment place (like sockets, qdiscs) takes
care of rcu protection and calls bpf_prog_put() after a grace period.
The programs stored inside prog_array may not be attached anywhere,
so prog_array needs to take care of preserving rcu protection.
Otherwise bpf_tail_call() will race with bpf_prog_put().
To solve that introduce bpf_prog_put_rcu() helper function and use
it in 3 places where unattached program can decrement refcnt:
closing program fd, deleting/replacing program in prog_array.

Fixes: 04fd61ab ("bpf: allow bpf programs to tail-call other bpf programs")
Reported-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d1f5f2bb
......@@ -123,7 +123,10 @@ struct bpf_prog_aux {
const struct bpf_verifier_ops *ops;
struct bpf_map **used_maps;
struct bpf_prog *prog;
struct work_struct work;
union {
struct work_struct work;
struct rcu_head rcu;
};
};
struct bpf_array {
......@@ -153,6 +156,7 @@ void bpf_register_map_type(struct bpf_map_type_list *tl);
struct bpf_prog *bpf_prog_get(u32 ufd);
void bpf_prog_put(struct bpf_prog *prog);
void bpf_prog_put_rcu(struct bpf_prog *prog);
struct bpf_map *bpf_map_get(struct fd f);
void bpf_map_put(struct bpf_map *map);
......
......@@ -202,7 +202,7 @@ static int prog_array_map_update_elem(struct bpf_map *map, void *key,
old_prog = xchg(array->prog + index, prog);
if (old_prog)
bpf_prog_put(old_prog);
bpf_prog_put_rcu(old_prog);
return 0;
}
......@@ -218,7 +218,7 @@ static int prog_array_map_delete_elem(struct bpf_map *map, void *key)
old_prog = xchg(array->prog + index, NULL);
if (old_prog) {
bpf_prog_put(old_prog);
bpf_prog_put_rcu(old_prog);
return 0;
} else {
return -ENOENT;
......
......@@ -432,6 +432,23 @@ static void free_used_maps(struct bpf_prog_aux *aux)
kfree(aux->used_maps);
}
static void __prog_put_rcu(struct rcu_head *rcu)
{
struct bpf_prog_aux *aux = container_of(rcu, struct bpf_prog_aux, rcu);
free_used_maps(aux);
bpf_prog_free(aux->prog);
}
/* version of bpf_prog_put() that is called after a grace period */
void bpf_prog_put_rcu(struct bpf_prog *prog)
{
if (atomic_dec_and_test(&prog->aux->refcnt)) {
prog->aux->prog = prog;
call_rcu(&prog->aux->rcu, __prog_put_rcu);
}
}
void bpf_prog_put(struct bpf_prog *prog)
{
if (atomic_dec_and_test(&prog->aux->refcnt)) {
......@@ -445,7 +462,7 @@ static int bpf_prog_release(struct inode *inode, struct file *filp)
{
struct bpf_prog *prog = filp->private_data;
bpf_prog_put(prog);
bpf_prog_put_rcu(prog);
return 0;
}
......
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