Without this, `state->speculative` is used after the cleanup cycles in push_stack() or push_async_cb() freed `env->cur_state` (i.e., `state`). Avoid this by relying on the short-circuit logic to only access `state` if the error is recoverable (and make sure it never is after push_*() failed). push_*() callers must always return an error for which error_recoverable_with_nospec(err) is false if push_*() returns NULL, otherwise we try to recover and access the stale `state`. This is only violated by sanitize_ptr_alu(), thus also fix this case to return -ENOMEM. state->speculative does not make sense if the error path of push_*() ran. In that case, `state->speculative && error_recoverable_with_nospec(err)` as a whole should already never evaluate to true (because all cases where push_stack() fails must return -ENOMEM/-EFAULT). As mentioned, this is only violated by the push_stack() call in sanitize_speculative_path() which returns -EACCES without [1] (through REASON_STACK in sanitize_err() after sanitize_ptr_alu()). To fix this, return -ENOMEM for REASON_STACK (which is also the behavior we will have after [1]). Checked that it fixes the syzbot reproducer as expected. [1] https://lore.kernel.org/all/20250603213232.339242-1-luis.gerhorst@xxxxxx/ Fixes: d6f1c85f2253 ("bpf: Fall back to nospec for Spectre v1") Reported-by: syzbot+b5eb72a560b8149a1885@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-by: Eduard Zingerman <eddyz87@xxxxxxxxx> Link: https://lore.kernel.org/all/38862a832b91382cddb083dddd92643bed0723b8.camel@xxxxxxxxx/ Signed-off-by: Luis Gerhorst <luis.gerhorst@xxxxxx> --- kernel/bpf/verifier.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b1f797616f20..d3bff0385a55 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14229,7 +14229,7 @@ static int sanitize_err(struct bpf_verifier_env *env, case REASON_STACK: verbose(env, "R%d could not be pushed for speculative verification, %s\n", dst, err); - break; + return -ENOMEM; default: verbose(env, "verifier internal error: unknown reason (%d)\n", reason); @@ -19753,7 +19753,7 @@ static int do_check(struct bpf_verifier_env *env) goto process_bpf_exit; err = do_check_insn(env, &do_print_state); - if (state->speculative && error_recoverable_with_nospec(err)) { + if (error_recoverable_with_nospec(err) && state->speculative) { /* Prevent this speculative path from ever reaching the * insn that would have been unsafe to execute. */ base-commit: 2d72dd14d77f31a7caa619fe0b889304844e612e -- 2.49.0
