Fix null termination bug #56
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mariomac
approved these changes
Apr 17, 2023
bpf/go_str.h
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| // put in a null terminator if we are not at max_size | ||
| if (size < max_size) { | ||
| char null = 0; | ||
| bpf_probe_read((char *)field + size, 1, &null); |
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Interesting... Is eBPF complaining if you just try field[size+1] = 0?
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I didn't t try it, but I can before I merge this. I thought with reserve/commit we had to use this approach since they can't prove we are allowed to access the memory. I'll try...
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Yeah that worked, I should've tried that first :).
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Thanks Mario! |
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Since we use the ring buffer reserve and commit strategy, we overwrite the memory directly to the ring buffer, avoiding two unnecessary operations, zero init on the stack for the structure and memcopy from the structure to the ring buffer. However, if the ring buffer gives us dirty pages of memory, we need to put a null terminator on the strings. Unlike using bpf_probe_read on a C99 initialized struct, we can't be sure we get zero initialized memory.
We only add the null terminator if we haven't written to the max size of the buffer. The go code that reads the C string looks for the null character and if it doesn't find it, it used the full array length as the size.