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bpf: Remove redundant free_verifier_state()/pop_stack()

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This patch removes duplicated code.

Eduard points out [1]:

    Same cleanup cycles are done in push_stack() and push_async_cb(),
    both functions are only reachable from do_check_common() via
    do_check() -> do_check_insn().

    Hence, I think that cur state should not be freed in push_*()
    functions and pop_stack() loop there is not needed.

This would also fix the 'symptom' for [2], but the issue also has a
simpler fix which was sent separately. This fix also makes sure the
push_*() callers always return an error for which
error_recoverable_with_nospec(err) is false. This is required because
otherwise we try to recover and access the stale `state`.

Moving free_verifier_state() and pop_stack(..., pop_log=false) to happen
after the bpf_vlog_reset() call in do_check_common() is fine because the
pop_stack() call that is moved does not call bpf_vlog_reset() with the
pop_log=false parameter.

[1] https://lore.kernel.org/all/b6931bd0dd72327c55287862f821ca6c4c3eb69a.camel@gmail.com/
[2] https://lore.kernel.org/all/68497853.050a0220.33aa0e.036a.GAE@google.com/

Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/all/b6931bd0dd72327c55287862f821ca6c4c3eb69a.camel@gmail.com/
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Luis Gerhorst <luis.gerhorst@fau.de>
Link: https://lore.kernel.org/r/20250613090157.568349-2-luis.gerhorst@fau.de
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Luis Gerhorst 2025-06-13 11:01:58 +02:00 committed by Alexei Starovoitov
parent 4a4b84ba9e
commit f66b4aaff2
1 changed files with 10 additions and 26 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

36
kernel/bpf/verifier.c
View file

@ -2097,7 +2097,7 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
elem = kzalloc(sizeof(struct bpf_verifier_stack_elem), GFP_KERNEL_ACCOUNT);
if (!elem)
goto err;
return NULL;
elem->insn_idx = insn_idx;
elem->prev_insn_idx = prev_insn_idx;
@ -2107,12 +2107,12 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
env->stack_size++;
err = copy_verifier_state(&elem->st, cur);
if (err)
goto err;
return NULL;
elem->st.speculative |= speculative;
if (env->stack_size > BPF_COMPLEXITY_LIMIT_JMP_SEQ) {
verbose(env, "The sequence of %d jumps is too complex.\n",
env->stack_size);
goto err;
return NULL;
}
if (elem->st.parent) {
++elem->st.parent->branches;
@ -2127,12 +2127,6 @@ static struct bpf_verifier_state *push_stack(struct bpf_verifier_env *env,
*/
}
return &elem->st;
err:
free_verifier_state(env->cur_state, true);
env->cur_state = NULL;
/* pop all elements and return */
while (!pop_stack(env, NULL, NULL, false));
return NULL;
}
#define CALLER_SAVED_REGS 6
@ -2864,7 +2858,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env,
elem = kzalloc(sizeof(struct bpf_verifier_stack_elem), GFP_KERNEL_ACCOUNT);
if (!elem)
goto err;
return NULL;
elem->insn_idx = insn_idx;
elem->prev_insn_idx = prev_insn_idx;
@ -2876,7 +2870,7 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env,
verbose(env,
"The sequence of %d jumps is too complex for async cb.\n",
env->stack_size);
goto err;
return NULL;
}
/* Unlike push_stack() do not copy_verifier_state().
* The caller state doesn't matter.
@ -2887,19 +2881,13 @@ static struct bpf_verifier_state *push_async_cb(struct bpf_verifier_env *env,
elem->st.in_sleepable = is_sleepable;
frame = kzalloc(sizeof(*frame), GFP_KERNEL_ACCOUNT);
if (!frame)
goto err;
return NULL;
init_func_state(env, frame,
BPF_MAIN_FUNC /* callsite */,
0 /* frameno within this callchain */,
subprog /* subprog number within this prog */);
elem->st.frame[0] = frame;
return &elem->st;
err:
free_verifier_state(env->cur_state, true);
env->cur_state = NULL;
/* pop all elements and return */
while (!pop_stack(env, NULL, NULL, false));
return NULL;
}
@ -22935,6 +22923,10 @@ static void free_states(struct bpf_verifier_env *env)
struct bpf_scc_info *info;
int i, j;
free_verifier_state(env->cur_state, true);
env->cur_state = NULL;
while (!pop_stack(env, NULL, NULL, false));
list_for_each_safe(pos, tmp, &env->free_list) {
sl = container_of(pos, struct bpf_verifier_state_list, node);
free_verifier_state(&sl->state, false);
@ -23086,14 +23078,6 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
ret = do_check(env);
out:
/* check for NULL is necessary, since cur_state can be freed inside
* do_check() under memory pressure.
*/
if (env->cur_state) {
free_verifier_state(env->cur_state, true);
env->cur_state = NULL;
}
while (!pop_stack(env, NULL, NULL, false));
if (!ret && pop_log)
bpf_vlog_reset(&env->log, 0);
free_states(env);