For all non-tracing helpers which formerly had ARG_PTR_TO_{LONG,INT} as input
arguments, zero the value for the case of an error as otherwise it could leak
memory. For tracing, it is not needed given CAP_PERFMON can already read all
kernel memory anyway hence bpf_get_func_arg() and bpf_get_func_ret() is skipped
in here.
Also, the MTU helpers mtu_len pointer value is being written but also read.
Technically, the MEM_UNINIT should not be there in order to always force init.
Removing MEM_UNINIT needs more verifier rework though: MEM_UNINIT right now
implies two things actually: i) write into memory, ii) memory does not have
to be initialized. If we lift MEM_UNINIT, it then becomes: i) read into memory,
ii) memory must be initialized. This means that for bpf_*_check_mtu() we're
readding the issue we're trying to fix, that is, it would then be able to
write back into things like .rodata BPF maps. Follow-up work will rework the
MEM_UNINIT semantics such that the intent can be better expressed. For now
just clear the *mtu_len on error path which can be lifted later again.
Fixes: 8a67f2de9b1d ("bpf: expose bpf_strtol and bpf_strtoul to all program types")
Fixes: d7a4cb9b6705 ("bpf: Introduce bpf_strtol and bpf_strtoul helpers")
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/e5edd241-59e7-5e39-0ee5-a51e31b6840a@xxxxxxxxxxxxx
---
v1 -> v2:
- only set *mtu_len in error path (Alexei)
v4 -> v5:
- extend explanation on MEM_UNINIT
kernel/bpf/helpers.c | 2 ++
kernel/bpf/syscall.c | 1 +
net/core/filter.c | 44 +++++++++++++++++++++++---------------------
3 files changed, 26 insertions(+), 21 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 5e97fdc6b20f..1a43d06eab28 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -523,6 +523,7 @@ BPF_CALL_4(bpf_strtol, const char *, buf, size_t, buf_len, u64, flags,
long long _res;
int err;
+ *res = 0;
err = __bpf_strtoll(buf, buf_len, flags, &_res);
if (err < 0)
return err;
@@ -548,6 +549,7 @@ BPF_CALL_4(bpf_strtoul, const char *, buf, size_t, buf_len, u64, flags,
bool is_negative;
int err;
+ *res = 0;
err = __bpf_strtoull(buf, buf_len, flags, &_res, &is_negative);
if (err < 0)
return err;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index a7cd3719e26a..593822d3d393 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5934,6 +5934,7 @@ static const struct bpf_func_proto bpf_sys_close_proto = {
BPF_CALL_4(bpf_kallsyms_lookup_name, const char *, name, int, name_sz, int, flags, u64 *, res)
{
+ *res = 0;
if (flags)
return -EINVAL;
diff --git a/net/core/filter.c b/net/core/filter.c
index d0550c87e520..e4a4454df5f9 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6262,20 +6262,25 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb,
int ret = BPF_MTU_CHK_RET_FRAG_NEEDED;
struct net_device *dev = skb->dev;
int skb_len, dev_len;
- int mtu;
+ int mtu = 0;
- if (unlikely(flags & ~(BPF_MTU_CHK_SEGS)))
- return -EINVAL;
+ if (unlikely(flags & ~(BPF_MTU_CHK_SEGS))) {
+ ret = -EINVAL;
+ goto out;
+ }
- if (unlikely(flags & BPF_MTU_CHK_SEGS && (len_diff || *mtu_len)))
- return -EINVAL;
+ if (unlikely(flags & BPF_MTU_CHK_SEGS && (len_diff || *mtu_len))) {
+ ret = -EINVAL;
+ goto out;
+ }
dev = __dev_via_ifindex(dev, ifindex);
- if (unlikely(!dev))
- return -ENODEV;
+ if (unlikely(!dev)) {
+ ret = -ENODEV;
+ goto out;
+ }
mtu = READ_ONCE(dev->mtu);
-
dev_len = mtu + dev->hard_header_len;
/* If set use *mtu_len as input, L3 as iph->tot_len (like fib_lookup) */
@@ -6293,15 +6298,12 @@ BPF_CALL_5(bpf_skb_check_mtu, struct sk_buff *, skb,
*/
if (skb_is_gso(skb)) {
ret = BPF_MTU_CHK_RET_SUCCESS;
-
if (flags & BPF_MTU_CHK_SEGS &&
!skb_gso_validate_network_len(skb, mtu))
ret = BPF_MTU_CHK_RET_SEGS_TOOBIG;
}
out:
- /* BPF verifier guarantees valid pointer */
*mtu_len = mtu;
-
return ret;
}
@@ -6311,19 +6313,21 @@ BPF_CALL_5(bpf_xdp_check_mtu, struct xdp_buff *, xdp,
struct net_device *dev = xdp->rxq->dev;
int xdp_len = xdp->data_end - xdp->data;
int ret = BPF_MTU_CHK_RET_SUCCESS;
- int mtu, dev_len;
+ int mtu = 0, dev_len;
/* XDP variant doesn't support multi-buffer segment check (yet) */
- if (unlikely(flags))
- return -EINVAL;
+ if (unlikely(flags)) {
+ ret = -EINVAL;
+ goto out;
+ }
dev = __dev_via_ifindex(dev, ifindex);
- if (unlikely(!dev))
- return -ENODEV;
+ if (unlikely(!dev)) {
+ ret = -ENODEV;
+ goto out;
+ }
mtu = READ_ONCE(dev->mtu);
-
- /* Add L2-header as dev MTU is L3 size */
dev_len = mtu + dev->hard_header_len;
/* Use *mtu_len as input, L3 as iph->tot_len (like fib_lookup) */
@@ -6333,10 +6337,8 @@ BPF_CALL_5(bpf_xdp_check_mtu, struct xdp_buff *, xdp,
xdp_len += len_diff; /* minus result pass check */
if (xdp_len > dev_len)
ret = BPF_MTU_CHK_RET_FRAG_NEEDED;
-
- /* BPF verifier guarantees valid pointer */
+out:
*mtu_len = mtu;
-
return ret;
}
--
2.43.0
