From: Xu Kuohai xukuohai@huawei.com

mainline inclusion from mainline-v6.12-rc1 commit 28ead3eaabc16ecc907cfb71876da028080f6356 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAYRIC CVE: CVE-2024-50063

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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bpf progs can be attached to kernel functions, and the attached functions can take different parameters or return different return values. If prog attached to one kernel function tail calls prog attached to another kernel function, the ctx access or return value verification could be bypassed.

For example, if prog1 is attached to func1 which takes only 1 parameter and prog2 is attached to func2 which takes two parameters. Since verifier assumes the bpf ctx passed to prog2 is constructed based on func2's prototype, verifier allows prog2 to access the second parameter from the bpf ctx passed to it. The problem is that verifier does not prevent prog1 from passing its bpf ctx to prog2 via tail call. In this case, the bpf ctx passed to prog2 is constructed from func1 instead of func2, that is, the assumption for ctx access verification is bypassed.

Another example, if BPF LSM prog1 is attached to hook file_alloc_security, and BPF LSM prog2 is attached to hook bpf_lsm_audit_rule_known. Verifier knows the return value rules for these two hooks, e.g. it is legal for bpf_lsm_audit_rule_known to return positive number 1, and it is illegal for file_alloc_security to return positive number. So verifier allows prog2 to return positive number 1, but does not allow prog1 to return positive number. The problem is that verifier does not prevent prog1 from calling prog2 via tail call. In this case, prog2's return value 1 will be used as the return value for prog1's hook file_alloc_security. That is, the return value rule is bypassed.

This patch adds restriction for tail call to prevent such bypasses.

Signed-off-by: Xu Kuohai xukuohai@huawei.com Link: https://lore.kernel.org/r/20240719110059.797546-4-xukuohai@huaweicloud.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Andrii Nakryiko andrii@kernel.org Conflicts: include/linux/bpf.h kernel/bpf/core.c [The conflicts were due to not merge commit f45d5b6ce2e8] Signed-off-by: Pu Lehui pulehui@huawei.com --- include/linux/bpf.h | 1 + kernel/bpf/core.c | 15 +++++++++++++++ 2 files changed, 16 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h index ba69705526eb..69ebb7d0a845 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -943,6 +943,7 @@ struct bpf_array_aux { * the same prog type and JITed flag. */ struct { + const struct btf_type *attach_func_proto; spinlock_t lock; enum bpf_prog_type type; bool jited; diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 7db8a815e835..054ff2000c0b 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1775,6 +1775,7 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *fp) { bool ret; + struct bpf_prog_aux *aux = fp->aux;

if (fp->kprobe_override) return false; @@ -1787,10 +1788,24 @@ bool bpf_prog_array_compatible(struct bpf_array *array, */ array->aux->owner.type = fp->type; array->aux->owner.jited = fp->jited; + array->aux->owner.attach_func_proto = aux->attach_func_proto; ret = true; } else { ret = array->aux->owner.type == fp->type && array->aux->owner.jited == fp->jited; + if (ret && + array->aux->owner.attach_func_proto != aux->attach_func_proto) { + switch (fp->type) { + case BPF_PROG_TYPE_TRACING: + case BPF_PROG_TYPE_LSM: + case BPF_PROG_TYPE_EXT: + case BPF_PROG_TYPE_STRUCT_OPS: + ret = false; + break; + default: + break; + } + } } spin_unlock(&array->aux->owner.lock); return ret;