diff options
| author | Luis Gerhorst <luis.gerhorst@fau.de> | 2025-06-11 23:07:28 +0200 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2025-06-12 16:52:43 -0700 |
| commit | 3d71b8b9abae68f6dfc434f779e1139370fbe891 (patch) | |
| tree | 7ed9ddc8433a75991eff97c70749eb19a28f63e3 /kernel | |
| parent | e3f6660b78b07a6662f65e44414d7d554e04801f (diff) | |
bpf: Fix state use-after-free on push_stack() err
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@fau.de/
Fixes: d6f1c85f2253 ("bpf: Fall back to nospec for Spectre v1")
Reported-by: syzbot+b5eb72a560b8149a1885@syzkaller.appspotmail.com
Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/all/38862a832b91382cddb083dddd92643bed0723b8.camel@gmail.com/
Signed-off-by: Luis Gerhorst <luis.gerhorst@fau.de>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250611210728.266563-1-luis.gerhorst@fau.de
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1d3277bf935e..14dd836acb13 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14293,7 +14293,7 @@ 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); @@ -19926,7 +19926,7 @@ 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. */ |