From e558cca217790286e799a8baacd1610bda31b261 Mon Sep 17 00:00:00 2001 From: Toke Høiland-Jørgensen Date: Mon, 5 Jan 2026 12:47:45 +0100 Subject: bpf, test_run: Subtract size of xdp_frame from allowed metadata size MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The xdp_frame structure takes up part of the XDP frame headroom, limiting the size of the metadata. However, in bpf_test_run, we don't take this into account, which makes it possible for userspace to supply a metadata size that is too large (taking up the entire headroom). If userspace supplies such a large metadata size in live packet mode, the xdp_update_frame_from_buff() call in xdp_test_run_init_page() call will fail, after which packet transmission proceeds with an uninitialised frame structure, leading to the usual Bad Stuff. The commit in the Fixes tag fixed a related bug where the second check in xdp_update_frame_from_buff() could fail, but did not add any additional constraints on the metadata size. Complete the fix by adding an additional check on the metadata size. Reorder the checks slightly to make the logic clearer and add a comment. Link: https://lore.kernel.org/r/fa2be179-bad7-4ee3-8668-4903d1853461@hust.edu.cn Fixes: b6f1f780b393 ("bpf, test_run: Fix packet size check for live packet mode") Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Signed-off-by: Toke Høiland-Jørgensen Reviewed-by: Amery Hung Link: https://lore.kernel.org/r/20260105114747.1358750-1-toke@redhat.com Signed-off-by: Alexei Starovoitov --- net/bpf/test_run.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'net') diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 655efac6f133..e6c0ad204b92 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -1294,8 +1294,6 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, batch_size = NAPI_POLL_WEIGHT; else if (batch_size > TEST_XDP_MAX_BATCH) return -E2BIG; - - headroom += sizeof(struct xdp_page_head); } else if (batch_size) { return -EINVAL; } @@ -1308,16 +1306,26 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, /* There can't be user provided data before the meta data */ if (ctx->data_meta || ctx->data_end > kattr->test.data_size_in || ctx->data > ctx->data_end || - unlikely(xdp_metalen_invalid(ctx->data)) || (do_live && (kattr->test.data_out || kattr->test.ctx_out))) goto free_ctx; - /* Meta data is allocated from the headroom */ - headroom -= ctx->data; meta_sz = ctx->data; + if (xdp_metalen_invalid(meta_sz) || meta_sz > headroom - sizeof(struct xdp_frame)) + goto free_ctx; + + /* Meta data is allocated from the headroom */ + headroom -= meta_sz; linear_sz = ctx->data_end; } + /* The xdp_page_head structure takes up space in each page, limiting the + * size of the packet data; add the extra size to headroom here to make + * sure it's accounted in the length checks below, but not in the + * metadata size check above. + */ + if (do_live) + headroom += sizeof(struct xdp_page_head); + max_linear_sz = PAGE_SIZE - headroom - tailroom; linear_sz = min_t(u32, linear_sz, max_linear_sz); -- cgit v1.2.3 From ec69daabe45256f98ac86c651b8ad1b2574489a7 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 8 Jan 2026 21:36:48 +0900 Subject: bpf: Fix reference count leak in bpf_prog_test_run_xdp() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit syzbot is reporting unregister_netdevice: waiting for sit0 to become free. Usage count = 2 problem. A debug printk() patch found that a refcount is obtained at xdp_convert_md_to_buff() from bpf_prog_test_run_xdp(). According to commit ec94670fcb3b ("bpf: Support specifying ingress via xdp_md context in BPF_PROG_TEST_RUN"), the refcount obtained by xdp_convert_md_to_buff() will be released by xdp_convert_buff_to_md(). Therefore, we can consider that the error handling path introduced by commit 1c1949982524 ("bpf: introduce frags support to bpf_prog_test_run_xdp()") forgot to call xdp_convert_buff_to_md(). Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84 Fixes: 1c1949982524 ("bpf: introduce frags support to bpf_prog_test_run_xdp()") Signed-off-by: Tetsuo Handa Reviewed-by: Toke Høiland-Jørgensen Link: https://lore.kernel.org/r/af090e53-9d9b-4412-8acb-957733b3975c@I-love.SAKURA.ne.jp Signed-off-by: Alexei Starovoitov --- net/bpf/test_run.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'net') diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index e6c0ad204b92..26cfcfdc45eb 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -1363,13 +1363,13 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, if (sinfo->nr_frags == MAX_SKB_FRAGS) { ret = -ENOMEM; - goto out; + goto out_put_dev; } page = alloc_page(GFP_KERNEL); if (!page) { ret = -ENOMEM; - goto out; + goto out_put_dev; } frag = &sinfo->frags[sinfo->nr_frags++]; @@ -1381,7 +1381,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, if (copy_from_user(page_address(page), data_in + size, data_len)) { ret = -EFAULT; - goto out; + goto out_put_dev; } sinfo->xdp_frags_size += data_len; size += data_len; @@ -1396,6 +1396,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, ret = bpf_test_run_xdp_live(prog, &xdp, repeat, batch_size, &duration); else ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, true); +out_put_dev: /* We convert the xdp_buff back to an xdp_md before checking the return * code so the reference count of any held netdevice will be decremented * even if the test run failed. -- cgit v1.2.3