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authorAlexei Starovoitov <ast@plumgrid.com>2015-05-28 19:26:02 -0700
committerDavid S. Miller <davem@davemloft.net>2015-05-31 00:27:51 -0700
commitabf2e7d6e2e315b32ee00067a69aaad2cf4e1b3f (patch)
tree073ee9134421f2ab9edcd226a48de1a4bea72554
parentd1f5f2bb91094c9e6f7c98610d637ffdaedef116 (diff)
downloadlinux-sh-abf2e7d6e2e315b32ee00067a69aaad2cf4e1b3f.tar.gz
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: 04fd61ab36ec ("bpf: allow bpf programs to tail-call other bpf programs") Reported-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/linux/bpf.h6
-rw-r--r--kernel/bpf/arraymap.c4
-rw-r--r--kernel/bpf/syscall.c19
3 files changed, 25 insertions, 4 deletions
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 8821b9a8689e..5f520f5f087e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -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);
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 614bcd4c1d74..cb31229a6fa4 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -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;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 98a69bd83069..a1b14d197a4f 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -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;
}