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Merge branch 'bpf-compare-iterator-types-during-state-pruning'

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Ning Ding says:

====================
bpf: Compare iterator types during state pruning

Iterator stack slots can be marked MEM_RCU or PTR_UNTRUSTED. The
STACK_ITER check in stacksafe() does not compare this type, so state
pruning can treat these states as equal and prune an unsafe path.

Compare the type and add a test where RCU protection has a gap.
---
Changes in v2:
- Convert the regression test to inline assembly so its verifier-sensitive
  control-flow layout is stable.
- Add Eduard Zingerman's Acked-by tag to patch 1.

v1: https://lore.kernel.org/bpf/20260807004320.134069-1-dingning04@gmail.com/
====================

Link: https://patch.msgid.link/20260811035955.132989-1-dingning04@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
This commit is contained in:
Eduard Zingerman
2026-08-11 14:57:01 -07:00
parent d114bb9893 81f209d5f7
commit 07cb86aa50
2 changed files with 48 additions and 1 deletions
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3
kernel/bpf/states.c
View File

@@ -812,7 +812,8 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
* infinite loop check triggering, see
* iter_active_depths_differ()
*/
if (old_reg->iter.btf != cur_reg->iter.btf ||
if (old_reg->type != cur_reg->type ||
old_reg->iter.btf != cur_reg->iter.btf ||
old_reg->iter.btf_id != cur_reg->iter.btf_id ||
old_reg->iter.state != cur_reg->iter.state ||
/* ignore {old_reg,cur_reg}->iter.depth, see above */

46
tools/testing/selftests/bpf/progs/iters_task_failure.c
View File

@@ -61,6 +61,52 @@ int BPF_PROG(iter_tasks_lock_and_unlock)
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
__failure __msg("expected an RCU CS when using bpf_iter_task_next")
__flag(BPF_F_TEST_STATE_FREQ)
int BPF_PROG(iter_tasks_rcu_state_pruning)
{
struct bpf_iter_task it;
asm volatile (
"call %[bpf_rcu_read_lock];"
"r1 = %[it];"
"r2 = 0;"
"r3 = 0;" /* BPF_TASK_ITER_ALL_PROCS */
"call %[bpf_iter_task_new];"
"call %[bpf_get_prandom_u32];"
"if w0 == 0 goto unprotected_%=;"
/* Keep the outer RCU lock active on the straight-line path. */
"call %[bpf_rcu_read_lock];"
"call %[bpf_rcu_read_unlock];"
"goto merge_%=;"
"unprotected_%=:"
/* Create an unprotected gap on the taken path. */
"call %[bpf_rcu_read_unlock];"
"call %[bpf_rcu_read_lock];"
"merge_%=: r1 = %[it];"
"call %[bpf_iter_task_next];"
"r1 = %[it];"
"call %[bpf_iter_task_destroy];"
"call %[bpf_rcu_read_unlock];"
:
: __imm_ptr(it),
__imm(bpf_get_prandom_u32),
__imm(bpf_iter_task_new),
__imm(bpf_iter_task_next),
__imm(bpf_iter_task_destroy),
__imm(bpf_rcu_read_lock),
__imm(bpf_rcu_read_unlock)
: __clobber_common
);
return 0;
}
SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
__failure __msg("expected an RCU CS when using bpf_iter_css_next")
int BPF_PROG(iter_css_lock_and_unlock)