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fix(driver/bpf): bpf_parse_readv_writev_bufs avoid overflow while reading readv/writev iovec struct #1733

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fix(driver/bpf): bpf_parse_readv_writev_bufs avoid overflow while reading readv/writev iovec struct #1733

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4 changes: 2 additions & 2 deletions driver/bpf/fillers.h
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Original file line number Diff line number Diff line change
Expand Up @@ -456,11 +456,11 @@ static __always_inline int bpf_parse_readv_writev_bufs(struct filler_data *data,

#ifdef BPF_FORBIDS_ZERO_ACCESS
if (to_read)
if (bpf_probe_read(&data->buf[off & SCRATCH_SIZE_HALF],
if (bpf_probe_read(&data->buf[off & SCRATCH_SIZE_HALF - 1],
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@gnosek gnosek Jan 15, 2021

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Parentheses? Is this expression (off & SCRATCH_SIZE_HALF) - 1 or off & (SCRATCH_SIZE_HALF - 1)?

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@fntlnz fntlnz Jan 15, 2021 •
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- has precedence over & and I confirm that the generated bpf bytecode is correct.

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@nathan-b nathan-b Jan 15, 2021

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Based on what you wrote above, is it possible that the intent of the code is (off & SCRATCH_SIZE_HALF) - 1?

((to_read - 1) & SCRATCH_SIZE_HALF) + 1,
iov[j].iov_base))
#else
if (bpf_probe_read(&data->buf[off & SCRATCH_SIZE_HALF],
if (bpf_probe_read(&data->buf[off & SCRATCH_SIZE_HALF - 1],
to_read & SCRATCH_SIZE_HALF,
iov[j].iov_base))
#endif
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