|author||Alexei Starovoitov <email@example.com>||2021-04-19 15:27:37 -0700|
|committer||Alexei Starovoitov <firstname.lastname@example.org>||2021-04-19 15:27:47 -0700|
Merge branch 'Add a snprintf eBPF helper'
Florent Revest says: ==================== We have a usecase where we want to audit symbol names (if available) in callback registration hooks. (ex: fentry/nf_register_net_hook) A few months back, I proposed a bpf_kallsyms_lookup series but it was decided in the reviews that a more generic helper, bpf_snprintf, would be more useful. This series implements the helper according to the feedback received in https://email@example.com/T/#u - A new arg type guarantees the NULL-termination of string arguments and lets us pass format strings in only one arg - A new helper is implemented using that guarantee. Because the format string is known at verification time, the format string validation is done by the verifier - To implement a series of tests for bpf_snprintf, the logic for marshalling variadic args in a fixed-size array is reworked as per: https://firstname.lastname@example.org/T/#u --- Changes in v5: - Fixed the bpf_printf_buf_used counter logic in try_get_fmt_tmp_buf - Added a couple of extra incorrect specifiers tests - Call test_snprintf_single__destroy unconditionally - Fixed a C++-style comment --- Changes in v4: - Moved bpf_snprintf, bpf_printf_prepare and bpf_printf_cleanup to kernel/bpf/helpers.c so that they get built without CONFIG_BPF_EVENTS - Added negative test cases (various invalid format strings) - Renamed put_fmt_tmp_buf() as bpf_printf_cleanup() - Fixed a mistake that caused temporary buffers to be unconditionally freed in bpf_printf_prepare - Fixed a mistake that caused missing 0 character to be ignored - Fixed a warning about integer to pointer conversion - Misc cleanups --- Changes in v3: - Simplified temporary buffer acquisition with try_get_fmt_tmp_buf() - Made zero-termination check more consistent - Allowed NULL output_buffer - Simplified the BPF_CAST_FMT_ARG macro - Three new test cases: number padding, simple string with no arg and string length extraction only with a NULL output buffer - Clarified helper's description for edge cases (eg: str_size == 0) - Lots of cosmetic changes --- Changes in v2: - Extracted the format validation/argument sanitization in a generic way for all printf-like helpers. - bpf_snprintf's str_size can now be 0 - bpf_snprintf is now exposed to all BPF program types - We now preempt_disable when using a per-cpu temporary buffer - Addressed a few cosmetic changes ==================== Acked-by: Andrii Nakryiko <email@example.com> Signed-off-by: Alexei Starovoitov <firstname.lastname@example.org>
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