Fix snprintf buffer too small in exec_ddprof()#499
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digits10 returns the number of decimal digits that round-trip through the type (floor(log10(2^31-1)) = 9), not the number of digits in the max value. The max pid_t (2,147,483,647) has 10 digits, so the buffer needs digits10 + 2 (max digits + NUL), not digits10 + 1. With digits10 + 1 (= 10 bytes), snprintf silently truncates 10-digit values, potentially passing a wrong PID to execve. Fixes DataDog#496
xroche
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February 27, 2026 20:12
r1viollet
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Mar 4, 2026
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Internal CI is OK on this ✅
Thank you for the fix
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What does this PR do?
Fix
snprintfbuffer sizing inexec_ddprof()(src/lib/dd_profiling.cc).digits10returns the number of decimal digits that can round-trip through the type (floor(log10(2^31 - 1))= 9), not the number of digits in the maximum value. The maxpid_t(2,147,483,647) has 10 digits, so the buffer needsdigits10 + 2(max digits + NUL), notdigits10 + 1.With the current size (10 bytes),
snprintfsilently truncates 10-digit values, potentially passing a wrong PID toexecve.Motivation
Same class of buffer sizing bug as #492 (off-by-one in
loader.c), but in the C++ library mode entry pointexec_ddprof().How to test the change?
The bug is currently mitigated by Linux PID limits (max 2^22 = 7 digits), so it doesn't trigger in practice. The fix is a straightforward buffer size correction.
Classification
Fixes #496