6.17-stable review patch. If anyone has any objections, please let me know.
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From: Eduard Zingerman eddyz87@gmail.com
[ Upstream commit b0c8e6d3d866b6a7f73877f71968dbffd27b7785 ]
The usage pattern for widen_imprecise_scalars() looks as follows:
prev_st = find_prev_entry(env, ...); queued_st = push_stack(...); widen_imprecise_scalars(env, prev_st, queued_st);
Where prev_st is an ancestor of the queued_st in the explored states tree. This ancestor is not guaranteed to have same allocated stack depth as queued_st. E.g. in the following case:
def main(): for i in 1..2: foo(i) // same callsite, differnt param
def foo(i): if i == 1: use 128 bytes of stack iterator based loop
Here, for a second 'foo' call prev_st->allocated_stack is 128, while queued_st->allocated_stack is much smaller. widen_imprecise_scalars() needs to take this into account and avoid accessing bpf_verifier_state->frame[*]->stack out of bounds.
Fixes: 2793a8b015f7 ("bpf: exact states comparison for iterator convergence checks") Reported-by: Emil Tsalapatis emil@etsalapatis.com Signed-off-by: Eduard Zingerman eddyz87@gmail.com Link: https://lore.kernel.org/r/20251114025730.772723-1-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2844adf4da61a..c3cdf2bf09aa4 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -8917,7 +8917,7 @@ static int widen_imprecise_scalars(struct bpf_verifier_env *env, struct bpf_verifier_state *cur) { struct bpf_func_state *fold, *fcur; - int i, fr; + int i, fr, num_slots;
reset_idmap_scratch(env); for (fr = old->curframe; fr >= 0; fr--) { @@ -8930,7 +8930,9 @@ static int widen_imprecise_scalars(struct bpf_verifier_env *env, &fcur->regs[i], &env->idmap_scratch);
- for (i = 0; i < fold->allocated_stack / BPF_REG_SIZE; i++) { + num_slots = min(fold->allocated_stack / BPF_REG_SIZE, + fcur->allocated_stack / BPF_REG_SIZE); + for (i = 0; i < num_slots; i++) { if (!is_spilled_reg(&fold->stack[i]) || !is_spilled_reg(&fcur->stack[i])) continue;