The error fallback does memcpy(dst, src, src_size) intending to store uncompressed data when compression fails, but this has three bugs: 1. dst has been advanced past the record header (and potentially past earlier compressed records), so the copy writes to the wrong offset in the output buffer. 2. src still points to the start of the input, not to the remaining uncompressed data at src + input.pos. On a second or later iteration, previously compressed data would be duplicated. 3. No check that dst_size >= src_size — if the remaining output space is smaller, this is an out-of-bounds write. Replace with return -1 after resetting the ZSTD compression context via ZSTD_initCStream(). The -1 propagates through zstd_compress() -> record__pushfn() -> perf_mmap__push() to the recording loop, which breaks out and terminates recording. Add an out_child_no_flush label in __cmd_record() so the mmap-read failure path skips the final record__mmap_read_all() flush — retrying the same read that just failed would just fail again, and the flush is only useful when the mmap data is intact but the control path (auxtrace, switch_output) had an error. Consolidate all error paths through a single 'reset' label to ensure the compression context is always reset on failure — including the output-buffer-full path, where a bare return without resetting would leave stale stream state that corrupts output if the caller retries. Also guard against process_header() writing the event header before the buffer-full check: add a sizeof(perf_event_header) pre-check so the callback never writes past the output buffer. Guard against ZSTD making no progress: if output.pos is zero after ZSTD_compressStream(), calling process_header(record, 0) would re-trigger header initialization, double-subtracting the header size from dst_size and underflowing the unsigned counter. Also fix two pre-existing issues in the same function: - Add a dst_size guard before subtracting the record header size: if the output buffer is nearly full, the unsigned dst_size -= size underflows to a huge value, causing ZSTD_compressStream to write past the buffer boundary. - Check the ZSTD_initCStream() return value and log an error if the context reset itself fails. Reported-by: sashiko-bot@kernel.org # Running on a local machine Reviewed-by: Ian Rogers <irogers@google.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Assisted-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>