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Questions - xdp-bpf

BPF verifier fails because of invalid access to packet

I am trying to get the server name from the SNI extension of a TLS hello packet in a XDP program. When I try to load it, I get the following error from the BPF verifier: invalid access to packet struc...
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user2233706

c

linux-kernel

ebpf

xdp-bpf

Votes: 0

Answers: 2

Latest Answer

I think I have found the core of the issue. The verifier tracks a couple of properties about variables which allow it to determine if the program might access data it shouldn't. One of these propertie...
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Dylan Reimerink

BPF verification error when trying to extract SNI from TLS packet

I am trying to get the server name from the SNI extension of a TLS hello packet in a XDP program. When I try to load it, I get the following error from the BPF verifier: math between pkt pointer and r...
test-img

user2233706

c

linux-kernel

ebpf

xdp-bpf

Votes: 0

Answers: 1

Latest Answer

TL;DR. From the verifier's point of view, ext_len is unbounded because of how it was computed. To allow you to add this value to the packet pointer, you need to add a new bound check. See below for fu...
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pchaigno

Need help in XDP program failing to load with error "R7 offset is outside of the packet"

I have written a XDP program that looks at the incoming SCTP packets. A SCTP packets can have multiple chunks into it. I am specifically interested in DATA chunks that contain the application layer pa...
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Pranav Chaudhary

filter

packet

ebpf

bpf

xdp-bpf

Votes: 0

Answers: 1

Latest Answer

TL;DR. You are hitting a corner-case limitation of the verifier. Changing the end of the for loop to the following may help. #define MAX_PACKET_OFF 0xffff ... nh->pos += size; if (nh->pos > M...
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pchaigno

Compiling program is not give me permission2 execute outpt of clang -o user.o|can't run user.o w/ sudo says command not found or sudo permision denied

So I compiled xdp program like /usr/lib/x86_64-linux-gnu/ sudo clang -Wall -L /usr/lib/x86_64-linux-gnu/ -I /usr/lib/usr/include/ -c af_xdp_user.c -o user.o or sudo clang -Wall -L /usr/lib/x86_64-...
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user786

c

linux

shared-libraries

ebpf

xdp-bpf

Votes: 0

Answers: 1

Latest Answer

I think you just have to add execute permissions to the file. Write this command in the terminal to do it: sudo chmod a+x user.o This command will add to all users execute permissions, so just typing...
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someoneCoding

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