[PATCH 5.19 229/717] selftests/xsk: Avoid use-after-free on ctx

Greg Kroah-Hartman
2022-10-22T07:57:18Z

From: Ian Rogers <irogers@google.com>

[ Upstream commit af515a5587b8f45f19e11657746e0c89411b0380 ]

The put lowers the reference count to 0 and frees ctx, reading it
afterwards is invalid. Move the put after the uses and determine the
last use by the reference count being 1.

Fixes: 39e940d4abfa ("selftests/xsk: Destroy BPF resources only when ctx refcount drops to 0")
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20220901202645.1463552-1-irogers@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/xsk.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 67dc010e9fe3..63954a2e213d 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -1228,15 +1228,15 @@ void xsk_socket__delete(struct xsk_socket *xsk)
ctx = xsk->ctx;
umem = ctx->umem;

- xsk_put_ctx(ctx, true);
-
- if (!ctx->refcount) {
+ if (ctx->refcount == 1) {
xsk_delete_bpf_maps(xsk);
close(ctx->prog_fd);
if (ctx->has_bpf_link)
close(ctx->link_fd);
}

+ xsk_put_ctx(ctx, true);
+
err = xsk_get_mmap_offsets(xsk->fd, &off);
if (!err) {
if (xsk->rx) {
--
2.35.1