In the Linux kernel, the following vulnerability has been resolved:

bpf: Avoid uninitialized value in BPF_CORE_READ_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
BPF_CRE_READ_BITFIELD macro, defined in bpf_core_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 __builtin_preserve_field_info returns unexpected values
for BPF_FIELD_BYTE_SIZE.

Tested in bpf-next master.
No regressions.

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-42161
• https://git.kernel.org/stable/c/009367099eb61a4fc2af44d4eb06b6b4de7de6db
• https://git.kernel.org/stable/c/3364c2ed1c241989847f19cf83e3db903ce689e3
• https://git.kernel.org/stable/c/7e5471b5efebc30dd0bc035cda86693a5c73d45f
• https://git.kernel.org/stable/c/a21d76bd0b0d39518e9a4c19f6cf7c042a974aff
• https://git.kernel.org/stable/c/b694989bb13ed5f166e633faa1eb0f21c6d261a6
• https://git.kernel.org/stable/c/ff941a8449e712eaf7efca1a13bfb9afd3d99fc2