path: root/net
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authorDaniel Borkmann <>2015-10-08 01:20:39 +0200
committerDavid S. Miller <>2015-10-08 05:26:39 -0700
commit3ad0040573b0c00f88488bc31958acd07a55ee2e (patch)
tree3afa13e8acbdf49a9f8c1a7993065c3836997a01 /net
parent897ece56e714a2cc64e6914cb89a362d7021b36e (diff)
bpf: split state from prandom_u32() and consolidate {c, e}BPF prngs
While recently arguing on a seccomp discussion that raw prandom_u32() access shouldn't be exposed to unpriviledged user space, I forgot the fact that SKF_AD_RANDOM extension actually already does it for some time in cBPF via commit 4cd3675ebf74 ("filter: added BPF random opcode"). Since prandom_u32() is being used in a lot of critical networking code, lets be more conservative and split their states. Furthermore, consolidate eBPF and cBPF prandom handlers to use the new internal PRNG. For eBPF, bpf_get_prandom_u32() was only accessible for priviledged users, but should that change one day, we also don't want to leak raw sequences through things like eBPF maps. One thought was also to have own per bpf_prog states, but due to ABI reasons this is not easily possible, i.e. the program code currently cannot access bpf_prog itself, and copying the rnd_state to/from the stack scratch space whenever a program uses the prng seems not really worth the trouble and seems too hacky. If needed, taus113 could in such cases be implemented within eBPF using a map entry to keep the state space, or get_random_bytes() could become a second helper in cases where performance would not be critical. Both sides can trigger a one-time late init via prandom_init_once() on the shared state. Performance-wise, there should even be a tiny gain as bpf_user_rnd_u32() saves one function call. The PRNG needs to live inside the BPF core since kernels could have a NET-less config as well. Signed-off-by: Daniel Borkmann <> Acked-by: Hannes Frederic Sowa <> Acked-by: Alexei Starovoitov <> Cc: Chema Gonzalez <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'net')
1 files changed, 2 insertions, 7 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 8f4603c712cd..342e6c8fc415 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -149,12 +149,6 @@ static u64 __get_raw_cpu_id(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
return raw_smp_processor_id();
-/* note that this only generates 32-bit random numbers */
-static u64 __get_random_u32(u64 ctx, u64 a, u64 x, u64 r4, u64 r5)
- return prandom_u32();
static u32 convert_skb_access(int skb_field, int dst_reg, int src_reg,
struct bpf_insn *insn_buf)
@@ -313,7 +307,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
*insn = BPF_EMIT_CALL(__get_raw_cpu_id);
- *insn = BPF_EMIT_CALL(__get_random_u32);
+ *insn = BPF_EMIT_CALL(bpf_user_rnd_u32);
+ bpf_user_rnd_init_once();