CVE-2024-49850

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

bpf: correctly handle malformed BPFCORETYPEIDLOCAL relos

In case of malformed relocation record of kind BPFCORETYPEIDLOCAL referencing a non-existing BTF type, function bpfcorecalcreloinsn would cause a null pointer deference.

Fix this by adding a proper check upper in call stack, as malformed relocation records could be passed from user space.

Simplest reproducer is a program:

r0 = 0
exit

With a single relocation record:

.insn_off = 0,          /* patch first instruction */
.type_id = 100500,      /* this type id does not exist */
.access_str_off = 6,    /* offset of string "0" */
.kind = BPF_CORE_TYPE_ID_LOCAL,

See the link for original reproducer or next commit for a test case.