diff mbox series

[bpf,3/5] bpf: Remove MEM_UNINIT from skb/xdp MTU helpers

Message ID 20241021152809.33343-3-daniel@iogearbox.net (mailing list archive)
State Accepted
Commit 14a3d3ef02ba53447d5112a2641aac0d10dc994f
Delegated to: BPF
Headers show
Series [bpf,1/5] bpf: Add MEM_WRITE attribute | expand

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Commit Message

Daniel Borkmann Oct. 21, 2024, 3:28 p.m. UTC 
We can now undo parts of 4b3786a6c539 ("bpf: Zero former ARG_PTR_TO_{LONG,INT}
args in case of error") as discussed in [0].

Given the BPF helpers now have MEM_WRITE tag, the MEM_UNINIT can be cleared.

The mtu_len is an input as well as output argument, meaning, the BPF program
has to set it to something. It cannot be uninitialized. Therefore, allowing
uninitialized memory and zeroing it on error would be odd. It was done as
an interim step in 4b3786a6c539 as the desired behavior could not have been
expressed before the introduction of MEM_WRITE tag.

Fixes: 4b3786a6c539 ("bpf: Zero former ARG_PTR_TO_{LONG,INT} args in case of error")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/a86eb76d-f52f-dee4-e5d2-87e45de3e16f@iogearbox.net [0]
---
 net/core/filter.c | 42 +++++++++++++++---------------------------
 1 file changed, 15 insertions(+), 27 deletions(-)

Comments

Kumar Kartikeya Dwivedi Oct. 22, 2024, 12:46 a.m. UTC | #1 
On Mon, 21 Oct 2024 at 17:28, Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> We can now undo parts of 4b3786a6c539 ("bpf: Zero former ARG_PTR_TO_{LONG,INT}
> args in case of error") as discussed in [0].
>
> Given the BPF helpers now have MEM_WRITE tag, the MEM_UNINIT can be cleared.
>
> The mtu_len is an input as well as output argument, meaning, the BPF program
> has to set it to something. It cannot be uninitialized. Therefore, allowing
> uninitialized memory and zeroing it on error would be odd. It was done as
> an interim step in 4b3786a6c539 as the desired behavior could not have been
> expressed before the introduction of MEM_WRITE tag.
>
> Fixes: 4b3786a6c539 ("bpf: Zero former ARG_PTR_TO_{LONG,INT} args in case of error")
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Link: https://lore.kernel.org/bpf/a86eb76d-f52f-dee4-e5d2-87e45de3e16f@iogearbox.net [0]
> ---

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
diff mbox series

Patch

diff --git a/net/core/filter.c b/net/core/filter.c
index 6be0c0b86049..26cc64f99d6a 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6281,24 +6281,16 @@  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 = 0;
+	int mtu, dev_len, skb_len;
 
-	if (unlikely(flags & ~(BPF_MTU_CHK_SEGS))) {
-		ret = -EINVAL;
-		goto out;
-	}
-
-	if (unlikely(flags & BPF_MTU_CHK_SEGS && (len_diff || *mtu_len))) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (unlikely(flags & ~(BPF_MTU_CHK_SEGS)))
+		return -EINVAL;
+	if (unlikely(flags & BPF_MTU_CHK_SEGS && (len_diff || *mtu_len)))
+		return -EINVAL;
 
 	dev = __dev_via_ifindex(dev, ifindex);
-	if (unlikely(!dev)) {
-		ret = -ENODEV;
-		goto out;
-	}
+	if (unlikely(!dev))
+		return -ENODEV;
 
 	mtu = READ_ONCE(dev->mtu);
 	dev_len = mtu + dev->hard_header_len;
@@ -6333,19 +6325,15 @@  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 = 0, dev_len;
+	int mtu, dev_len;
 
 	/* XDP variant doesn't support multi-buffer segment check (yet) */
-	if (unlikely(flags)) {
-		ret = -EINVAL;
-		goto out;
-	}
+	if (unlikely(flags))
+		return -EINVAL;
 
 	dev = __dev_via_ifindex(dev, ifindex);
-	if (unlikely(!dev)) {
-		ret = -ENODEV;
-		goto out;
-	}
+	if (unlikely(!dev))
+		return -ENODEV;
 
 	mtu = READ_ONCE(dev->mtu);
 	dev_len = mtu + dev->hard_header_len;
@@ -6357,7 +6345,7 @@  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;
-out:
+
 	*mtu_len = mtu;
 	return ret;
 }
@@ -6368,7 +6356,7 @@  static const struct bpf_func_proto bpf_skb_check_mtu_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type      = ARG_PTR_TO_CTX,
 	.arg2_type      = ARG_ANYTHING,
-	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
+	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_WRITE | MEM_ALIGNED,
 	.arg3_size	= sizeof(u32),
 	.arg4_type      = ARG_ANYTHING,
 	.arg5_type      = ARG_ANYTHING,
@@ -6380,7 +6368,7 @@  static const struct bpf_func_proto bpf_xdp_check_mtu_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type      = ARG_PTR_TO_CTX,
 	.arg2_type      = ARG_ANYTHING,
-	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_UNINIT | MEM_WRITE | MEM_ALIGNED,
+	.arg3_type      = ARG_PTR_TO_FIXED_SIZE_MEM | MEM_WRITE | MEM_ALIGNED,
 	.arg3_size	= sizeof(u32),
 	.arg4_type      = ARG_ANYTHING,
 	.arg5_type      = ARG_ANYTHING,