In the Linux kernel, the following vulnerability has been resolved:
bpf: Avoid uninitialized value in BPFCOREREAD_BITFIELD
[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 bpfcore_read.h as:
[...]
unsigned long long val; \
[...] \
switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
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 BPFFIELDBYTE_SIZE.
Tested in bpf-next master. No regressions.