CVE-2020-27418

In the Linux kernel's BPF subsystem, mark_fastcall_pattern_for_call() must ensure that a matched "spill; call; fill" instruction series is not interrupted by a jump. Otherwise the rewrite applied by bpf_remove_fastcall_spills_fills() is unsound. The fix records instructions targeted by jumps in insn_aux_data[*].jump_target and uses this flag to stop growing a pattern.

In the Linux kernel's BPF subsystem, in_rbtree_lock_required_cb() only checks the innermost verifier frame, so rbtree callback restrictions disappear in a nested static subprogram call frame. The subprogram can unlock the tree, remove and drop the node being compared, then relock, leading to freed memory being linked into the tree.

In the Linux kernel's BPF subsystem, bpf_btf_find_by_name_kind() returns a new BTF object fd through __btf_new_fd(), which reaches anon_inode_getfd() that can sleep while allocating or expanding the current task fd table. The helper prototype does not set might_sleep, so the verifier allows the helper in non-sleepable contexts such as BPF timer callbacks.

In the Linux kernel, a BPF verifier vulnerability affects stack helpers that may block on filesystem reads (e.g., resolving build IDs) but were not marked as sleepable. The verifier could still allow these helpers from non-sleepable regions such as RCU or preemption-disabled sections.

In the Linux kernel, the BPF verifier mishandled legacy packet-load instructions (BPF_LD_ABS/BPF_LD_IND) reached from callbacks, triggering a verifier bug warning and an -EFAULT on BPF_PROG_LOAD. A privileged program loader could trigger this issue.

In the Linux kernel, the BPF verifier incorrectly inferred that a pointer with an unbounded offset is non-NULL based solely on its type. As a result, a BPF program could pass verification while a NULL pointer dereference occurred at runtime.

In the Linux kernel, the BPF verifier could resurrect a scalar id dropped by collect_linked_regs() because snapshots of compared registers were taken before linked registers were collected. This could lead to range inconsistencies and precision propagation issues.

In the Linux kernel, the BPF verifier incorrectly predicted the outcome of pointer vs zero comparisons in JMP32 instructions, failing to distinguish BPF_JMP from BPF_JMP32 comparisons. This led to incorrect inference that a jump is always taken.

In the Linux kernel, the BPF verifier did not mark the zero register as precise for a register-form NULL check. As a result, one path was pruned and the program could dereference a zero pointer at runtime.

In the Linux kernel, the BPF verifier did not require the MEM_PERCPU flag for stores to percpu kptr fields, accepting both plain bpf_obj_new() allocations and kernel pointers. This could lead to arbitrary kernel read/write or invalid address relocation.