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Message-Id: <20171009122715.19010-1-shmulik@nsof.io>
Date: Mon, 9 Oct 2017 15:27:15 +0300
From: Shmulik Ladkani <shmulik@...f.io>
To: Pablo Neira Ayuso <pablo@...filter.org>,
netfilter-devel@...r.kernel.org
Cc: netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>,
shmulik@...f.io, Rafael Buchbinder <rafi@....ms>,
Shmulik Ladkani <shmulik.ladkani@...il.com>,
Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH v2] netfilter: xt_bpf: Fix XT_BPF_MODE_FD_PINNED mode of 'xt_bpf_info_v1'
From: Shmulik Ladkani <shmulik.ladkani@...il.com>
Commit 2c16d6033264 ("netfilter: xt_bpf: support ebpf") introduced
support for attaching an eBPF object by an fd, with the
'bpf_mt_check_v1' ABI expecting the '.fd' to be specified upon each
IPT_SO_SET_REPLACE call.
However this breaks subsequent iptables calls:
# iptables -A INPUT -m bpf --object-pinned /sys/fs/bpf/xxx -j ACCEPT
# iptables -A INPUT -s 5.6.7.8 -j ACCEPT
iptables: Invalid argument. Run `dmesg' for more information.
That's because iptables works by loading exising rules using
IPT_SO_GET_ENTRIES to userspace, then issuing IPT_SO_SET_REPLACE with
the replacement set.
However, the loaded 'xt_bpf_info_v1' has an arbitrary '.fd' number
(from the initial "iptables -m bpf" invocation) - so when 2nd invocation
occurs, userspace passes a bogus fd number, which leads to
'bpf_mt_check_v1' to fail.
One suggested solution [1] was to hack iptables userspace, to perform a
"entries fixup" immediatley after IPT_SO_GET_ENTRIES, by opening a new,
process-local fd per every 'xt_bpf_info_v1' entry seen.
However, in [2] both Pablo Neira Ayuso and Willem de Bruijn suggested to
depricate the xt_bpf_info_v1 ABI dealing with pinned ebpf objects.
This fix changes the XT_BPF_MODE_FD_PINNED behavior to ignore the given
'.fd' and instead perform an in-kernel lookup for the bpf object given
the provided '.path'.
It also defines an alias for the XT_BPF_MODE_FD_PINNED mode, named
XT_BPF_MODE_PATH_PINNED, to better reflect the fact that the user is
expected to provide the path of the pinned object.
Existing XT_BPF_MODE_FD_ELF behavior (non-pinned fd mode) is preserved.
References: [1] https://marc.info/?l=netfilter-devel&m=150564724607440&w=2
[2] https://marc.info/?l=netfilter-devel&m=150575727129880&w=2
Cc: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Willem de Bruijn <willemb@...gle.com>
Reported-by: Rafael Buchbinder <rafi@....ms>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@...il.com>
---
v2: Fix xt_bpf.c compilation if CONFIG_BPF_SYSCALL=n
---
include/linux/bpf.h | 5 +++++
include/uapi/linux/netfilter/xt_bpf.h | 1 +
kernel/bpf/inode.c | 1 +
net/netfilter/xt_bpf.c | 22 ++++++++++++++++++++--
4 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a67daea731ab..a49b321a1262 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -407,6 +407,11 @@ static inline void __bpf_prog_uncharge(struct user_struct *user, u32 pages)
{
}
+static inline int bpf_obj_get_user(const char __user *pathname)
+{
+ return -EOPNOTSUPP;
+}
+
static inline struct net_device *__dev_map_lookup_elem(struct bpf_map *map,
u32 key)
{
diff --git a/include/uapi/linux/netfilter/xt_bpf.h b/include/uapi/linux/netfilter/xt_bpf.h
index b97725af2ac0..da161b56c79e 100644
--- a/include/uapi/linux/netfilter/xt_bpf.h
+++ b/include/uapi/linux/netfilter/xt_bpf.h
@@ -23,6 +23,7 @@ enum xt_bpf_modes {
XT_BPF_MODE_FD_PINNED,
XT_BPF_MODE_FD_ELF,
};
+#define XT_BPF_MODE_PATH_PINNED XT_BPF_MODE_FD_PINNED
struct xt_bpf_info_v1 {
__u16 mode;
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index e833ed914358..be1dde967208 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -363,6 +363,7 @@ int bpf_obj_get_user(const char __user *pathname)
putname(pname);
return ret;
}
+EXPORT_SYMBOL_GPL(bpf_obj_get_user);
static void bpf_evict_inode(struct inode *inode)
{
diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c
index 38986a95216c..29123934887b 100644
--- a/net/netfilter/xt_bpf.c
+++ b/net/netfilter/xt_bpf.c
@@ -8,6 +8,7 @@
*/
#include <linux/module.h>
+#include <linux/syscalls.h>
#include <linux/skbuff.h>
#include <linux/filter.h>
#include <linux/bpf.h>
@@ -49,6 +50,22 @@ static int __bpf_mt_check_fd(int fd, struct bpf_prog **ret)
return 0;
}
+static int __bpf_mt_check_path(const char *path, struct bpf_prog **ret)
+{
+ mm_segment_t oldfs = get_fs();
+ int retval, fd;
+
+ set_fs(KERNEL_DS);
+ fd = bpf_obj_get_user(path);
+ set_fs(oldfs);
+ if (fd < 0)
+ return fd;
+
+ retval = __bpf_mt_check_fd(fd, ret);
+ sys_close(fd);
+ return retval;
+}
+
static int bpf_mt_check(const struct xt_mtchk_param *par)
{
struct xt_bpf_info *info = par->matchinfo;
@@ -66,9 +83,10 @@ static int bpf_mt_check_v1(const struct xt_mtchk_param *par)
return __bpf_mt_check_bytecode(info->bpf_program,
info->bpf_program_num_elem,
&info->filter);
- else if (info->mode == XT_BPF_MODE_FD_PINNED ||
- info->mode == XT_BPF_MODE_FD_ELF)
+ else if (info->mode == XT_BPF_MODE_FD_ELF)
return __bpf_mt_check_fd(info->fd, &info->filter);
+ else if (info->mode == XT_BPF_MODE_PATH_PINNED)
+ return __bpf_mt_check_path(info->path, &info->filter);
else
return -EINVAL;
}
--
2.14.2
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