[PATCHv2] net: bpf: reject invalid shifts
From: Eric Dumazet <hidden>
Date: 2016-01-12 19:48:38
Also in:
netdev
On Tue, 2016-01-12 at 20:17 +0100, Rabin Vincent wrote:
On ARM64, a BUG() is triggered in the eBPF JIT if a filter with a constant shift that can't be encoded in the immediate field of the UBFM/SBFM instructions is passed to the JIT. Since these shifts amounts, which are negative or >= regsize, are invalid, reject them in the eBPF verifier and the classic BPF filter checker, for all architectures.
Hmm...
quoted hunk ↗ jump to hunk
diff --git a/net/core/filter.c b/net/core/filter.c index 672eefbfbe99..37157c4c1a78 100644 --- a/net/core/filter.c +++ b/net/core/filter.c@@ -777,6 +777,11 @@ static int bpf_check_classic(const struct sock_filter *filter, if (ftest->k == 0) return -EINVAL; break; + case BPF_ALU | BPF_LSH | BPF_K: + case BPF_ALU | BPF_RSH | BPF_K: + if (ftest->k >= 32) + return -EINVAL; + break; case BPF_LD | BPF_MEM: case BPF_LDX | BPF_MEM: case BPF_ST:
These weak filters used to have undefined behavior, maybe in a never taken branch, and will now fail hard, possibly breaking old applications. I believe we should add a one time warning to give a clue to poor users hitting this problem. Not everybody has perfect BPF filters, since most of the time they were hand coded.