In the Linux kernel, the following vulnerability has been resolved: bpf: Avoid uninitialized value in BPFCOREREADBITFIELD [Changes from V1: - Use a default branch in the switch statement to initialize val'.] GCC warns that
val' may be used uninitialized in the BPFCREREADBITFIELD macro, defined in bpfcoreread.h as: [...] unsigned long long val; \ [...] \ switch (_CORERELO(s, field, BYTESIZE)) { \ case 1: val = *(const unsigned char *)p; break; \ case 2: val = *(const unsigned short *)p; break; \ case 4: val = *(const unsigned int *)p; break; \ case 8: val = *(const unsigned long long *)p; break; \ } \ [...] val; \ } \ This patch adds a default entry in the switch statement that sets `val' to zero in order to avoid the warning, and random values to be used in case _builtinpreservefieldinfo returns unexpected values for BPFFIELDBYTESIZE. Tested in bpf-next master. No regressions.