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bpf: Don't return EINVAL from {get,set}sockopt when optlen > PAGE_SIZE 

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: 0d01da6afc ("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
This commit is contained in:
Stanislav Fomichev 2020-06-16 18:04:14 -07:00 committed by Alexei Starovoitov
parent 99c51064fb
commit d8fe449a9c
1 changed files with 33 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
kernel/bpf/cgroup.c
View File

@ -1276,16 +1276,23 @@ 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)
@ -1319,13 +1326,13 @@ 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;
}
@ -1353,9 +1360,15 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
/* export any potential modifications */
*level = ctx.level;
*optname = ctx.optname;
/* optlen == 0 from BPF indicates that we should
* use original userspace data.
*/
if (ctx.optlen != 0) {
*optlen = ctx.optlen;
*kernel_optval = ctx.optval;
}
}
out:
if (ret)
@ -1385,12 +1398,12 @@ 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
@ -1404,10 +1417,8 @@ 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;
}
@ -1436,11 +1447,13 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
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;