From: Stanislav Fomichev sdf@google.com
[ Upstream commit d8fe449a9c51a37d844ab607e14e2f5c657d3cf2 ]
Attaching to these hooks can break iptables because its optval is usually quite big, or at least bigger than the current PAGE_SIZE limit. David also mentioned some SCTP options can be big (around 256k).
For such optvals we expose only the first PAGE_SIZE bytes to the BPF program. BPF program has two options: 1. Set ctx->optlen to 0 to indicate that the BPF's optval should be ignored and the kernel should use original userspace value. 2. Set ctx->optlen to something that's smaller than the PAGE_SIZE.
v5: * use ctx->optlen == 0 with trimmed buffer (Alexei Starovoitov) * update the docs accordingly
v4: * use temporary buffer to avoid optval == optval_end == NULL; this removes the corner case in the verifier that might assume non-zero PTR_TO_PACKET/PTR_TO_PACKET_END.
v3: * don't increase the limit, bypass the argument
v2: * proper comments formatting (Jakub Kicinski)
Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks") Signed-off-by: Stanislav Fomichev sdf@google.com Signed-off-by: Alexei Starovoitov ast@kernel.org Cc: David Laight David.Laight@ACULAB.COM Link: https://lore.kernel.org/bpf/20200617010416.93086-1-sdf@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/cgroup.c | 53 ++++++++++++++++++++++++++++----------------- 1 file changed, 33 insertions(+), 20 deletions(-)
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 869e2e1860e84..b701af27a7799 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -966,16 +966,23 @@ static bool __cgroup_bpf_prog_array_is_empty(struct cgroup *cgrp,
static int sockopt_alloc_buf(struct bpf_sockopt_kern *ctx, int max_optlen) { - if (unlikely(max_optlen > PAGE_SIZE) || max_optlen < 0) + if (unlikely(max_optlen < 0)) return -EINVAL;
+ if (unlikely(max_optlen > PAGE_SIZE)) { + /* We don't expose optvals that are greater than PAGE_SIZE + * to the BPF program. + */ + max_optlen = PAGE_SIZE; + } + ctx->optval = kzalloc(max_optlen, GFP_USER); if (!ctx->optval) return -ENOMEM;
ctx->optval_end = ctx->optval + max_optlen;
- return 0; + return max_optlen; }
static void sockopt_free_buf(struct bpf_sockopt_kern *ctx) @@ -1009,13 +1016,13 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level, */ max_optlen = max_t(int, 16, *optlen);
- ret = sockopt_alloc_buf(&ctx, max_optlen); - if (ret) - return ret; + max_optlen = sockopt_alloc_buf(&ctx, max_optlen); + if (max_optlen < 0) + return max_optlen;
ctx.optlen = *optlen;
- if (copy_from_user(ctx.optval, optval, *optlen) != 0) { + if (copy_from_user(ctx.optval, optval, min(*optlen, max_optlen)) != 0) { ret = -EFAULT; goto out; } @@ -1043,8 +1050,14 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level, /* export any potential modifications */ *level = ctx.level; *optname = ctx.optname; - *optlen = ctx.optlen; - *kernel_optval = ctx.optval; + + /* optlen == 0 from BPF indicates that we should + * use original userspace data. + */ + if (ctx.optlen != 0) { + *optlen = ctx.optlen; + *kernel_optval = ctx.optval; + } }
out: @@ -1076,12 +1089,12 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, __cgroup_bpf_prog_array_is_empty(cgrp, BPF_CGROUP_GETSOCKOPT)) return retval;
- ret = sockopt_alloc_buf(&ctx, max_optlen); - if (ret) - return ret; - ctx.optlen = max_optlen;
+ max_optlen = sockopt_alloc_buf(&ctx, max_optlen); + if (max_optlen < 0) + return max_optlen; + if (!retval) { /* If kernel getsockopt finished successfully, * copy whatever was returned to the user back @@ -1095,10 +1108,8 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, goto out; }
- if (ctx.optlen > max_optlen) - ctx.optlen = max_optlen; - - if (copy_from_user(ctx.optval, optval, ctx.optlen) != 0) { + if (copy_from_user(ctx.optval, optval, + min(ctx.optlen, max_optlen)) != 0) { ret = -EFAULT; goto out; } @@ -1127,10 +1138,12 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level, goto out; }
- if (copy_to_user(optval, ctx.optval, ctx.optlen) || - put_user(ctx.optlen, optlen)) { - ret = -EFAULT; - goto out; + if (ctx.optlen != 0) { + if (copy_to_user(optval, ctx.optval, ctx.optlen) || + put_user(ctx.optlen, optlen)) { + ret = -EFAULT; + goto out; + } }
ret = ctx.retval;