Commit c2002f98 authored by Daniel Borkmann's avatar Daniel Borkmann Committed by David S. Miller

bpf: fix checking xdp_adjust_head on tail calls

Commit 17bedab2 ("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: 17bedab2 ("bpf: xdp: Allow head adjustment in XDP prog")
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 6b1bb01b
...@@ -623,6 +623,7 @@ static void fixup_bpf_calls(struct bpf_prog *prog) ...@@ -623,6 +623,7 @@ static void fixup_bpf_calls(struct bpf_prog *prog)
* in the program array. * in the program array.
*/ */
prog->cb_access = 1; prog->cb_access = 1;
prog->xdp_adjust_head = 1;
/* mark bpf_tail_call as different opcode /* mark bpf_tail_call as different opcode
* to avoid conditional branch in * to avoid conditional branch in
......
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