From: Kris Van Hees kris.van.hees@oracle.com
[ Upstream commit a5bebc4f00dee47113eed48098c68e88b5ba70e8 ]
Commit bfc6bb74e4f1 ("bpf: Implement verifier support for validation of async callbacks.") added support for BPF_FUNC_timer_set_callback to the __check_func_call() function. The test in __check_func_call() is flaweed because it can mis-interpret a regular BPF-to-BPF pseudo-call as a BPF_FUNC_timer_set_callback callback call.
Consider the conditional in the code:
if (insn->code == (BPF_JMP | BPF_CALL) && insn->imm == BPF_FUNC_timer_set_callback) {
The BPF_FUNC_timer_set_callback has value 170. This means that if you have a BPF program that contains a pseudo-call with an instruction delta of 170, this conditional will be found to be true by the verifier, and it will interpret the pseudo-call as a callback. This leads to a mess with the verification of the program because it makes the wrong assumptions about the nature of this call.
Solution: include an explicit check to ensure that insn->src_reg == 0. This ensures that calls cannot be mis-interpreted as an async callback call.
Fixes: bfc6bb74e4f1 ("bpf: Implement verifier support for validation of async callbacks.") Signed-off-by: Kris Van Hees kris.van.hees@oracle.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20220105210150.GH1559@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 45d5e71cd64e6..d48000b90eb8a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5965,6 +5965,7 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn }
if (insn->code == (BPF_JMP | BPF_CALL) && + insn->src_reg == 0 && insn->imm == BPF_FUNC_timer_set_callback) { struct bpf_verifier_state *async_cb;