CVE-2025-38060: backport fix series

Hi,

Please consider this backport series for CVE-2025-38060 to 6.6.y.

Apply the patches in this order:
1. bpf: copy_verifier_state() should copy 'loop_entry' field (fix)
2. bpf: abort verification if env->cur_state->loop_entry != NULL (correction)

Patch 1 preserves loop_entry when copying verifier state, keeping cloned loop states consistent with their originals.

Patch 2 aborts verification with -EFAULT when loop_entry is unexpectedly set instead of clearing the pointer and continuing with corrupted state. The code changes in both patches are identical to upstream.

The complete fix is already present in 6.12.y, 6.18.y and 7.2.y.

Build-tested only as part of a cumulative 6.6.y series on x86_64 (allmodconfig, CONFIG_WERROR=y); no runtime testing.

An LLM assisted with preparing these backports.

Thanks,
Artem Dinaburg

From: Eduard Zingerman <[email protected]>

[ Upstream commit bbbc02b7445ebfda13e4847f4f1413c6480a85a9 ]

The bpf_verifier_state.loop_entry state should be copied by copy_verifier_state(). Otherwise, .loop_entry values from unrelated states would poison env->cur_state.

Additionally, env->stack should not contain any states with .loop_entry != NULL. The states in env->stack are yet to be verified, while .loop_entry is set for states that reached an equivalent state. This means that env->cur_state->loop_entry should always be NULL after pop_stack().

See the selftest in the next commit for an example of the program that is not safe yet is accepted by verifier w/o this fix.

This change has some verification performance impact for selftests:

File                                Program                       Insns (A)  Insns (B)  Insns   (DIFF)  States (A)  States (B)  States (DIFF)
----------------------------------  ----------------------------  ---------  ---------  --------------  ----------  ----------  -------------
arena_htab.bpf.o                    arena_htab_llvm                     717        426  -291 (-40.59%)          57          37  -20 (-35.09%)
arena_htab_asm.bpf.o                arena_htab_asm                      597        445  -152 (-25.46%)          47          37  -10 (-21.28%)
arena_list.bpf.o                    arena_list_del                      309        279    -30 (-9.71%)          23          14   -9 (-39.13%)
iters.bpf.o                         iter_subprog_check_stacksafe        155        141    -14 (-9.03%)          15          14    -1 (-6.67%)
iters.bpf.o                         iter_subprog_iters                 1094       1003    -91 (-8.32%)          88          83    -5 (-5.68%)
iters.bpf.o                         loop_state_deps2                    479        725  +246 (+51.36%)          46          63  +17 (+36.96%)
kmem_cache_iter.bpf.o               open_coded_iter                      63         59     -4 (-6.35%)           7           6   -1 (-14.29%)
verifier_bits_iter.bpf.o            max_words                            92         84     -8 (-8.70%)           8           7   -1 (-12.50%)
verifier_iterating_callbacks.bpf.o  cond_break2                         113        107     -6 (-5.31%)          12          12    +0 (+0.00%)

And significant negative impact for sched_ext:

File               Program                 Insns (A)  Insns (B)  Insns         (DIFF)  States (A)  States (B)  States      (DIFF)
-----------------  ----------------------  ---------  ---------  --------------------  ----------  ----------  ------------------
bpf.bpf.o          lavd_init                    7039      14723      +7684 (+109.16%)         490        1139     +649 (+132.45%)
bpf.bpf.o          layered_dispatch            11485      10548         -937 (-8.16%)         848         762       -86 (-10.14%)
bpf.bpf.o          layered_dump                 7422    1000001  +992579 (+13373.47%)         681       31178  +30497 (+4478.27%)
bpf.bpf.o          layered_enqueue             16854      71127     +54273 (+322.02%)        1611        6450    +4839 (+300.37%)
bpf.bpf.o          p2dq_dispatch                 665        791        +126 (+18.95%)          68          78       +10 (+14.71%)
bpf.bpf.o          p2dq_init                    2343       2980        +637 (+27.19%)         201         237       +36 (+17.91%)
bpf.bpf.o          refresh_layer_cpumasks      16487     674760   +658273 (+3992.68%)        1770       65370  +63600 (+3593.22%)
bpf.bpf.o          rusty_select_cpu             1937      40872    +38935 (+2010.07%)         177        3210   +3033 (+1713.56%)
scx_central.bpf.o  central_dispatch              636       2687      +2051 (+322.48%)          63         227     +164 (+260.32%)
scx_nest.bpf.o     nest_init                     636        815        +179 (+28.14%)          60          73       +13 (+21.67%)
scx_qmap.bpf.o     qmap_dispatch                2393       3580       +1187 (+49.60%)         196         253       +57 (+29.08%)
scx_qmap.bpf.o     qmap_dump                     233        318         +85 (+36.48%)          22          30        +8 (+36.36%)
scx_qmap.bpf.o     qmap_init                   16367      17436        +1069 (+6.53%)         603         669       +66 (+10.95%)

Note 'layered_dump' program, which now hits 1M instructions limit. This impact would be mitigated in the next patch.

---
Hi,

Please consider this backport of the fix for CVE-2025-38060 to 6.6.y.

The code changes are identical to upstream.

The complete fix is already present in 6.12.y, 6.18.y and 7.2.y.

Build-tested only as part of a cumulative 6.6.y series on x86_64 (allmodconfig, CONFIG_WERROR=y); no runtime testing.

Thanks,
Artem Dinaburg

 kernel/bpf/verifier.c |    3 +++
 1 file changed, 3 insertions(+)

index 778a68bfb91dd4e765252cfb1bacb4b658d1381b..c00113e691955a6c9c6caa56007ccf90ce9b87d8 100644
@@ -1804,6 +1804,7 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state,
 	dst_state->dfs_depth = src->dfs_depth;
 	dst_state->callback_unroll_depth = src->callback_unroll_depth;
 	dst_state->used_as_loop_entry = src->used_as_loop_entry;
+	dst_state->loop_entry = src->loop_entry;
 	for (i = 0; i <= src->curframe; i++) {
 		dst = dst_state->frame[i];
 		if (!dst) {

@@ -17561,6 +17562,8 @@ process_bpf_exit:
 						return err;
 					break;
 				} else {
+					if (WARN_ON_ONCE(env->cur_state->loop_entry))
+						env->cur_state->loop_entry = NULL;
 					do_print_state = true;
 					continue;
 				}

From: Eduard Zingerman <[email protected]>

[ Upstream commit f3c2d243a36ef23be07bc2bce7c6a5cb6e07d9e3 ]

In addition to warning abort verification with -EFAULT. If env->cur_state->loop_entry != NULL something is irrecoverably buggy.

---
Hi,

Please consider this backport of the corrective follow-up for CVE-2025-38060 to 6.6.y.

The code changes are identical to upstream.

The complete fix is already present in 6.12.y, 6.18.y and 7.2.y.

Build-tested only as part of a cumulative 6.6.y series on x86_64 (allmodconfig, CONFIG_WERROR=y); no runtime testing.

Thanks,
Artem Dinaburg

 kernel/bpf/verifier.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

index c00113e691955a6c9c6caa56007ccf90ce9b87d8..37abde03f174ef5c0a47317d9b9d19eeaeb0ccd2 100644
@@ -17562,8 +17562,10 @@ process_bpf_exit:
 						return err;
 					break;
 				} else {
-					if (WARN_ON_ONCE(env->cur_state->loop_entry))
-						env->cur_state->loop_entry = NULL;
+					if (WARN_ON_ONCE(env->cur_state->loop_entry)) {
+						verbose(env, "verifier bug: env->cur_state->loop_entry != NULL\n");
+						return -EFAULT;
+					}
 					do_print_state = true;
 					continue;
 				}

Queued for 6.6, thanks.

Thanks,
Sasha