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[bpf-next,v1,6/7] bpf: Use memmove for bpf_dynptr_{read,write}

Message ID 20221115000130.1967465-7-memxor@gmail.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series Dynptr refactorings | expand

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Commit Message

Kumar Kartikeya Dwivedi Nov. 15, 2022, 12:01 a.m. UTC 
It may happen that destination buffer memory overlaps with memory dynptr
points to. Hence, we must use memmove to correctly copy from dynptr to
destination buffer, or source buffer to dynptr.

This actually isn't a problem right now, as memcpy implementation falls
back to memmove on detecting overlap and warns about it, but we
shouldn't be relying on that.

Acked-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/helpers.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

David Vernet Nov. 17, 2022, 11:51 p.m. UTC | #1 
On Tue, Nov 15, 2022 at 05:31:29AM +0530, Kumar Kartikeya Dwivedi wrote:
> It may happen that destination buffer memory overlaps with memory dynptr
> points to. Hence, we must use memmove to correctly copy from dynptr to
> destination buffer, or source buffer to dynptr.
> 
> This actually isn't a problem right now, as memcpy implementation falls
> back to memmove on detecting overlap and warns about it, but we
> shouldn't be relying on that.
> 
> Acked-by: Joanne Koong <joannelkoong@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---

Good call, thanks for this.

Acked-by: David Vernet <void@manifault.com>

>  kernel/bpf/helpers.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 714f5c9d0c1f..1099ed1e7712 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -1489,7 +1489,7 @@ BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
>  	if (err)
>  		return err;
>  
> -	memcpy(dst, src->data + src->offset + offset, len);
> +	memmove(dst, src->data + src->offset + offset, len);

Can you add a comment here and in bpf_dynptr_write() which explain why
memmove is needed?

>  
>  	return 0;
>  }
> @@ -1517,7 +1517,7 @@ BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
>  	if (err)
>  		return err;
>  
> -	memcpy(dst->data + dst->offset + offset, src, len);
> +	memmove(dst->data + dst->offset + offset, src, len);
>  
>  	return 0;
>  }
> -- 
> 2.38.1
>
diff mbox series

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 714f5c9d0c1f..1099ed1e7712 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1489,7 +1489,7 @@  BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
 	if (err)
 		return err;
 
-	memcpy(dst, src->data + src->offset + offset, len);
+	memmove(dst, src->data + src->offset + offset, len);
 
 	return 0;
 }
@@ -1517,7 +1517,7 @@  BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
 	if (err)
 		return err;
 
-	memcpy(dst->data + dst->offset + offset, src, len);
+	memmove(dst->data + dst->offset + offset, src, len);
 
 	return 0;
 }