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| author | Eduard Zingerman <eddyz87@gmail.com> | 2026-09-04 01:33:20 -0700 |
|---|---|---|
| committer | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2026-09-04 12:58:03 +0200 |
| commit | 73a98f96811e2cb0f4210b1caa8cb322f92f2a2b (patch) | |
| tree | e9508662e72a041bf48995a47ee68f3141356408 | |
| parent | 6752b90ccfb378e311e428932facf37c8625abae (diff) | |
| download | linux-73a98f96811e2cb0f4210b1caa8cb322f92f2a2b.tar.gz linux-73a98f96811e2cb0f4210b1caa8cb322f92f2a2b.zip | |
bpf: Don't resurrect a scalar id dropped by collect_linked_regs()
check_cond_jmp_op() copies the compared registers into
env->{false,true}_reg{1,2} before collect_linked_regs() runs and copies
those snapshots back into both branch states afterwards.
collect_linked_regs() records at most LINKED_REGS_MAX members of a
linked registers group in the jump history and calls clear_scalar_id()
for every member that does not fit. The compared register is not exempt
from that.
As a consequence, sync_linked_regs() might adjust ranges for more
registers than bpf_bt_sync_linked_regs() can propagate precision to.
Collect the linked registers before the snapshots are taken instead.
This might lead to some unnecessary clear_scalar_id's, but from
previous testing situations with many linked registers are
extremely rare.
Fixes: ec1d77cb0ee9 ("bpf: Use bpf_verifier_env buffers for reg_set_min_max")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260904083325.2083493-3-eddyz87@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
| -rw-r--r-- | kernel/bpf/verifier.c | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index faf1c8ff243d..1fb0c832611c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16898,6 +16898,16 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, return err; } + /* + * Collect the linked registers before env->{true,false}_reg{1,2} setup, + * otherwise ids dropped by collect_linked_regs() would be resurrected + * when env->{true,false}_reg{1,2} are copied back. + */ + if (BPF_SRC(insn->code) == BPF_X && src_reg->type == SCALAR_VALUE && src_reg->id) + collect_linked_regs(env, this_branch, src_reg->id, &linked_regs); + if (dst_reg->type == SCALAR_VALUE && dst_reg->id) + collect_linked_regs(env, this_branch, dst_reg->id, &linked_regs); + is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32; env->false_reg1 = *dst_reg; env->false_reg2 = *src_reg; @@ -16952,10 +16962,6 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, * 'this_branch' and 'other_branch' share this history * if parent state is created. */ - if (BPF_SRC(insn->code) == BPF_X && src_reg->type == SCALAR_VALUE && src_reg->id) - collect_linked_regs(env, this_branch, src_reg->id, &linked_regs); - if (dst_reg->type == SCALAR_VALUE && dst_reg->id) - collect_linked_regs(env, this_branch, dst_reg->id, &linked_regs); if (linked_regs.cnt > 1) { err = bpf_push_jmp_history(env, this_branch, 0, 0, 0, linked_regs_pack(&linked_regs)); if (err) |