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xdp: Support specifying expected existing program when attaching XDP

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While it is currently possible for userspace to specify that an existing
XDP program should not be replaced when attaching to an interface, there is
no mechanism to safely replace a specific XDP program with another.

This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be
set along with IFLA_XDP_FD. If set, the kernel will check that the program
currently loaded on the interface matches the expected one, and fail the
operation if it does not. This corresponds to a 'cmpxchg' memory operation.
Setting the new attribute with a negative value means that no program is
expected to be attached, which corresponds to setting the UPDATE_IF_NOEXIST
flag.

A new companion flag, XDP_FLAGS_REPLACE, is also added to explicitly
request checking of the EXPECTED_FD attribute. This is needed for userspace
to discover whether the kernel supports the new attribute.

Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/bpf/158515700640.92963.3551295145441017022.stgit@toke.dk
This commit is contained in:
Toke Høiland-Jørgensen 2020-03-25 18:23:26 +01:00 committed by Alexei Starovoitov
parent e9ff9d5254
commit 92234c8f15
4 changed files with 39 additions and 7 deletions
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2
include/linux/netdevice.h
View File

@ -3768,7 +3768,7 @@ struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
typedef int (*bpf_op_t)(struct net_device *dev, struct netdev_bpf *bpf);
int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
int fd, u32 flags);
int fd, int expected_fd, u32 flags);
u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
enum bpf_netdev_command cmd);
int xdp_umem_query(struct net_device *dev, u16 queue_id);

4
include/uapi/linux/if_link.h
View File

@ -972,11 +972,12 @@ enum {
#define XDP_FLAGS_SKB_MODE (1U << 1)
#define XDP_FLAGS_DRV_MODE (1U << 2)
#define XDP_FLAGS_HW_MODE (1U << 3)
#define XDP_FLAGS_REPLACE (1U << 4)
#define XDP_FLAGS_MODES (XDP_FLAGS_SKB_MODE | \
XDP_FLAGS_DRV_MODE | \
XDP_FLAGS_HW_MODE)
#define XDP_FLAGS_MASK (XDP_FLAGS_UPDATE_IF_NOEXIST | \
XDP_FLAGS_MODES)
XDP_FLAGS_MODES | XDP_FLAGS_REPLACE)
/* These are stored into IFLA_XDP_ATTACHED on dump. */
enum {
@ -996,6 +997,7 @@ enum {
IFLA_XDP_DRV_PROG_ID,
IFLA_XDP_SKB_PROG_ID,
IFLA_XDP_HW_PROG_ID,
IFLA_XDP_EXPECTED_FD,
__IFLA_XDP_MAX,
};

26
net/core/dev.c
View File

@ -8655,15 +8655,17 @@ static void dev_xdp_uninstall(struct net_device *dev)
* @dev: device
* @extack: netlink extended ack
* @fd: new program fd or negative value to clear
* @expected_fd: old program fd that userspace expects to replace or clear
* @flags: xdp-related flags
*
* Set or clear a bpf program for a device
*/
int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
int fd, u32 flags)
int fd, int expected_fd, u32 flags)
{
const struct net_device_ops *ops = dev->netdev_ops;
enum bpf_netdev_command query;
u32 prog_id, expected_id = 0;
struct bpf_prog *prog = NULL;
bpf_op_t bpf_op, bpf_chk;
bool offload;
@ -8684,15 +8686,29 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
if (bpf_op == bpf_chk)
bpf_chk = generic_xdp_install;
if (fd >= 0) {
u32 prog_id;
prog_id = __dev_xdp_query(dev, bpf_op, query);
if (flags & XDP_FLAGS_REPLACE) {
if (expected_fd >= 0) {
prog = bpf_prog_get_type_dev(expected_fd,
BPF_PROG_TYPE_XDP,
bpf_op == ops->ndo_bpf);
if (IS_ERR(prog))
return PTR_ERR(prog);
expected_id = prog->aux->id;
bpf_prog_put(prog);
}
if (prog_id != expected_id) {
NL_SET_ERR_MSG(extack, "Active program does not match expected");
return -EEXIST;
}
}
if (fd >= 0) {
if (!offload && __dev_xdp_query(dev, bpf_chk, XDP_QUERY_PROG)) {
NL_SET_ERR_MSG(extack, "native and generic XDP can't be active at the same time");
return -EEXIST;
}
prog_id = __dev_xdp_query(dev, bpf_op, query);
if ((flags & XDP_FLAGS_UPDATE_IF_NOEXIST) && prog_id) {
NL_SET_ERR_MSG(extack, "XDP program already attached");
return -EBUSY;
@ -8715,7 +8731,7 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
return 0;
}
} else {
if (!__dev_xdp_query(dev, bpf_op, query))
if (!prog_id)
return 0;
}

14
net/core/rtnetlink.c
View File

@ -1872,7 +1872,9 @@ static const struct nla_policy ifla_port_policy[IFLA_PORT_MAX+1] = {
};
static const struct nla_policy ifla_xdp_policy[IFLA_XDP_MAX + 1] = {
[IFLA_XDP_UNSPEC] = { .strict_start_type = IFLA_XDP_EXPECTED_FD },
[IFLA_XDP_FD] = { .type = NLA_S32 },
[IFLA_XDP_EXPECTED_FD] = { .type = NLA_S32 },
[IFLA_XDP_ATTACHED] = { .type = NLA_U8 },
[IFLA_XDP_FLAGS] = { .type = NLA_U32 },
[IFLA_XDP_PROG_ID] = { .type = NLA_U32 },
@ -2799,8 +2801,20 @@ static int do_setlink(const struct sk_buff *skb,
}
if (xdp[IFLA_XDP_FD]) {
int expected_fd = -1;
if (xdp_flags & XDP_FLAGS_REPLACE) {
if (!xdp[IFLA_XDP_EXPECTED_FD]) {
err = -EINVAL;
goto errout;
}
expected_fd =
nla_get_s32(xdp[IFLA_XDP_EXPECTED_FD]);
}
err = dev_change_xdp_fd(dev, extack,
nla_get_s32(xdp[IFLA_XDP_FD]),
expected_fd,
xdp_flags);
if (err)
goto errout;