Re: [PATCH] net: filter: make JITs zero A for SKF_AD_ALU_XOR_X

On 01/05/2016 04:23 PM, Rabin Vincent wrote:

The SKF_AD_ALU_XOR_X ancillary is not like the other ancillary data
instructions since it XORs A with X while all the others replace A with
some loaded value.  All the BPF JITs fail to clear A if this is used as
the first instruction in a filter.  This was found using american fuzzy
lop.

Add a helper to determine if A needs to be cleared given the first
instruction in a filter, and use this in the JITs.  Except for ARM, the
rest have only been compile-tested.

Fixes: 3480593131e0 ("net: filter: get rid of BPF_S_* enum")
Signed-off-by: Rabin Vincent <redacted>

Excellent catch, thanks a lot! The fix looks good to me and should
go to -net tree.

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

If you're interested, feel free to add a small test case for the
SKF_AD_ALU_XOR_X issue to lib/test_bpf.c for -net-next tree. Thanks!