4.14-stable review patch. If anyone has any objections, please let me know.
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From: John Fastabend john.fastabend@gmail.com
[ Upstream commit 3d9e952697de89b53227f06d4241f275eb99cfc4 ]
When a program is attached to a map we increment the program refcnt to ensure that the program is not removed while it is potentially being referenced from sockmap side. However, if this same program also references the map (this is a reasonably common pattern in my programs) then the verifier will also increment the maps refcnt from the verifier. This is to ensure the map doesn't get garbage collected while the program has a reference to it.
So we are left in a state where the map holds the refcnt on the program stopping it from being removed and releasing the map refcnt. And vice versa the program holds a refcnt on the map stopping it from releasing the refcnt on the prog.
All this is fine as long as users detach the program while the map fd is still around. But, if the user omits this detach command we are left with a dangling map we can no longer release.
To resolve this when the map fd is released decrement the program references and remove any reference from the map to the program. This fixes the issue with possibly dangling map and creates a user side API constraint. That is, the map fd must be held open for programs to be attached to a map.
Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support") Signed-off-by: John Fastabend john.fastabend@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/sockmap.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
--- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c @@ -601,11 +601,6 @@ static void sock_map_free(struct bpf_map } rcu_read_unlock();
- if (stab->bpf_verdict) - bpf_prog_put(stab->bpf_verdict); - if (stab->bpf_parse) - bpf_prog_put(stab->bpf_parse); - sock_map_remove_complete(stab); }
@@ -877,6 +872,19 @@ static int sock_map_update_elem(struct b return err; }
+static void sock_map_release(struct bpf_map *map, struct file *map_file) +{ + struct bpf_stab *stab = container_of(map, struct bpf_stab, map); + struct bpf_prog *orig; + + orig = xchg(&stab->bpf_parse, NULL); + if (orig) + bpf_prog_put(orig); + orig = xchg(&stab->bpf_verdict, NULL); + if (orig) + bpf_prog_put(orig); +} + const struct bpf_map_ops sock_map_ops = { .map_alloc = sock_map_alloc, .map_free = sock_map_free, @@ -884,6 +892,7 @@ const struct bpf_map_ops sock_map_ops = .map_get_next_key = sock_map_get_next_key, .map_update_elem = sock_map_update_elem, .map_delete_elem = sock_map_delete_elem, + .map_release = sock_map_release, };
BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, bpf_sock,