2022-09-01 20:57:05

by Ian Rogers

Subject: [PATCH v1] selftests/xsk: Avoid use-after-free on ctx

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 <[email protected]>
---
tools/testing/selftests/bpf/xsk.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/xsk.c b/tools/testing/selftests/bpf/xsk.c
index f2721a4ae7c5..0b3ff49c740d 100644
--- a/tools/testing/selftests/bpf/xsk.c
+++ b/tools/testing/selftests/bpf/xsk.c
@@ -1237,15 +1237,15 @@ 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) {
--
2.37.2.789.g6183377224-goog

2022-09-02 06:53:02

by Magnus Karlsson

Subject: Re: [PATCH v1] selftests/xsk: Avoid use-after-free on ctx

On Thu, Sep 1, 2022 at 10:56 PM Ian Rogers <[email protected]> wrote:
>
> 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.

Thanks for spotting and fixing this Ian.

Acked-by: Magnus Karlsson <[email protected]>

> Fixes: 39e940d4abfa ("selftests/xsk: Destroy BPF resources only when ctx refcount drops to 0")
> Signed-off-by: Ian Rogers <[email protected]>
> ---
> tools/testing/selftests/bpf/xsk.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/xsk.c b/tools/testing/selftests/bpf/xsk.c
> index f2721a4ae7c5..0b3ff49c740d 100644
> --- a/tools/testing/selftests/bpf/xsk.c
> +++ b/tools/testing/selftests/bpf/xsk.c
> @@ -1237,15 +1237,15 @@ 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) {
> --
> 2.37.2.789.g6183377224-goog
>

2022-09-02 14:52:01

by patchwork-bot+netdevbpf

Subject: Re: [PATCH v1] selftests/xsk: Avoid use-after-free on ctx

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[email protected]>:

On Thu, 1 Sep 2022 13:26:45 -0700 you wrote:
> 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 <[email protected]>
>
> [...]

Here is the summary with links:
- [v1] selftests/xsk: Avoid use-after-free on ctx
https://git.kernel.org/bpf/bpf-next/c/af515a5587b8

You are awesome, thank you!
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