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    Subject[PATCH 5.10 110/390] selftests/xsk: Avoid use-after-free on ctx
    Date
    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 e8745f646371..fa1f8faf7dfe 100644
    --- a/tools/lib/bpf/xsk.c
    +++ b/tools/lib/bpf/xsk.c
    @@ -930,13 +930,13 @@ 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);
    }

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


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