From c2002f983767ea0a53acbb3e21f771e7a7e2ed28 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 17 Apr 2017 03:12:07 +0200 Subject: [PATCH] bpf: fix checking xdp_adjust_head on tail calls Commit 17bedab27231 ("bpf: xdp: Allow head adjustment in XDP prog") added the xdp_adjust_head bit to the BPF prog in order to tell drivers that the program that is to be attached requires support for the XDP bpf_xdp_adjust_head() helper such that drivers not supporting this helper can reject the program. There are also drivers that do support the helper, but need to check for xdp_adjust_head bit in order to move packet metadata prepended by the firmware away for making headroom. For these cases, the current check for xdp_adjust_head bit is insufficient since there can be cases where the program itself does not use the bpf_xdp_adjust_head() helper, but tail calls into another program that uses bpf_xdp_adjust_head(). As such, the xdp_adjust_head bit is still set to 0. Since the first program has no control over which program it calls into, we need to assume that bpf_xdp_adjust_head() helper is used upon tail calls. Thus, for the very same reasons in cb_access, set the xdp_adjust_head bit to 1 when the main program uses tail calls. Fixes: 17bedab27231 ("bpf: xdp: Allow head adjustment in XDP prog") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Cc: Martin KaFai Lau Signed-off-by: David S. Miller --- kernel/bpf/syscall.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index ee5c969d5963..821f9e807de5 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -623,6 +623,7 @@ static void fixup_bpf_calls(struct bpf_prog *prog) * in the program array. */ prog->cb_access = 1; + prog->xdp_adjust_head = 1; /* mark bpf_tail_call as different opcode * to avoid conditional branch in -- 2.20.1