From e5995bc7e2ba1a0d444f806016d2e4ea91c032d0 Mon Sep 17 00:00:00 2001 From: Alexander Lobakin Date: Thu, 16 Mar 2023 18:50:50 +0100 Subject: bpf, test_run: fix crashes due to XDP frame overwriting/corruption MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit syzbot and Ilya faced the splats when %XDP_PASS happens for bpf_test_run after skb PP recycling was enabled for {__,}xdp_build_skb_from_frame(): BUG: kernel NULL pointer dereference, address: 0000000000000d28 RIP: 0010:memset_erms+0xd/0x20 arch/x86/lib/memset_64.S:66 [...] Call Trace: __finalize_skb_around net/core/skbuff.c:321 [inline] __build_skb_around+0x232/0x3a0 net/core/skbuff.c:379 build_skb_around+0x32/0x290 net/core/skbuff.c:444 __xdp_build_skb_from_frame+0x121/0x760 net/core/xdp.c:622 xdp_recv_frames net/bpf/test_run.c:248 [inline] xdp_test_run_batch net/bpf/test_run.c:334 [inline] bpf_test_run_xdp_live+0x1289/0x1930 net/bpf/test_run.c:362 bpf_prog_test_run_xdp+0xa05/0x14e0 net/bpf/test_run.c:1418 [...] This happens due to that it calls xdp_scrub_frame(), which nullifies xdpf->data. bpf_test_run code doesn't reinit the frame when the XDP program doesn't adjust head or tail. Previously, %XDP_PASS meant the page will be released from the pool and returned to the MM layer, but now it does return to the Pool with the nullified xdpf->data, which doesn't get reinitialized then. So, in addition to checking whether the head and/or tail have been adjusted, check also for a potential XDP frame corruption. xdpf->data is 100% affected and also xdpf->flags is the field closest to the metadata / frame start. Checking for these two should be enough for non-extreme cases. Fixes: 9c94bbf9a87b ("xdp: recycle Page Pool backed skbs built from XDP frames") Reported-by: syzbot+e1d1b65f7c32f2a86a9f@syzkaller.appspotmail.com Link: https://lore.kernel.org/bpf/000000000000f1985705f6ef2243@google.com Reported-by: Ilya Leoshkevich Link: https://lore.kernel.org/bpf/e07dd94022ad5731705891b9487cc9ed66328b94.camel@linux.ibm.com Signed-off-by: Alexander Lobakin Acked-by: Toke Høiland-Jørgensen Tested-by: Ilya Leoshkevich Link: https://lore.kernel.org/r/20230316175051.922550-2-aleksander.lobakin@intel.com Signed-off-by: Alexei Starovoitov --- net/bpf/test_run.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'net/bpf') diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 71226f68270d..8d6b31209bd6 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -208,6 +208,16 @@ static void xdp_test_run_teardown(struct xdp_test_data *xdp) kfree(xdp->skbs); } +static bool frame_was_changed(const struct xdp_page_head *head) +{ + /* xdp_scrub_frame() zeroes the data pointer, flags is the last field, + * i.e. has the highest chances to be overwritten. If those two are + * untouched, it's most likely safe to skip the context reset. + */ + return head->frm.data != head->orig_ctx.data || + head->frm.flags != head->orig_ctx.flags; +} + static bool ctx_was_changed(struct xdp_page_head *head) { return head->orig_ctx.data != head->ctx.data || @@ -217,7 +227,7 @@ static bool ctx_was_changed(struct xdp_page_head *head) static void reset_ctx(struct xdp_page_head *head) { - if (likely(!ctx_was_changed(head))) + if (likely(!frame_was_changed(head) && !ctx_was_changed(head))) return; head->ctx.data = head->orig_ctx.data; -- cgit v1.2.3