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[scudo] Only read urandom if getrandom syscall isn't available. #161889

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Oct 6, 2025
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[scudo] Only read urandom if getrandom syscall isn't available. #161889

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6 changes: 6 additions & 0 deletions compiler-rt/lib/scudo/standalone/linux.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,12 @@ bool getRandom(void *Buffer, uptr Length, UNUSED bool Blocking) {
syscall(SYS_getrandom, Buffer, Length, Blocking ? 0 : GRND_NONBLOCK);
if (ReadBytes == static_cast<ssize_t>(Length))
return true;
// If this system call is not implemented in the kernel, then we will try
// and use /dev/urandom. Otherwise, if the syscall fails, return false
// assuming that trying to read /dev/urandom will cause a delay waiting for
// the random data to be usable.
if (errno != ENOSYS)
return false;
#endif // defined(SYS_getrandom)
// Up to 256 bytes, a read off /dev/urandom will not be interrupted.
// Blocking is moot here, O_NONBLOCK has no effect when opening /dev/urandom.
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