[PATCH bpf] bpf: roll back stream capacity when allocation fails

[Jianlin Shi]

bpf_stream_push_str() accounts the string length before allocating a
stream element. If the allocation fails, the length remains charged even
though no element is queued and therefore cannot be released by a reader.
Repeated failures can exhaust the stream capacity permanently until the
BPF program is freed.

Roll back the capacity charge when creating the stream element fails.

Fixes: 5ab154f1463a ("bpf: Introduce BPF standard streams")
Signed-off-by: Jianlin Shi <shijianlin11@xxxxxxxxxxx>
---
 kernel/bpf/stream.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/stream.c b/kernel/bpf/stream.c
index be9ce98e9..4b8a74b91 100644
--- a/kernel/bpf/stream.c
+++ b/kernel/bpf/stream.c
@@ -79,7 +79,14 @@ static int bpf_stream_push_str(struct bpf_stream *stream, const char *str, int l
 {
 	int ret = bpf_stream_consume_capacity(stream, len);
 
-	return ret ?: __bpf_stream_push_str(&stream->log, str, len);
+	if (ret)
+		return ret;
+
+	ret = __bpf_stream_push_str(&stream->log, str, len);
+	if (ret)
+		atomic_sub(len, &stream->capacity);
+
+	return ret;
 }
 
 static struct bpf_stream *bpf_stream_get(enum bpf_stream_id stream_id, struct bpf_prog_aux *aux)
-- 
2.43.0