6.12-stable review patch. If anyone has any objections, please let me know.
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From: Kumar Kartikeya Dwivedi memxor@gmail.com
[ Upstream commit 69772f509e084ec6bca12dbcdeeeff41b0103774 ]
Inside mark_stack_slot_misc, we should not upgrade STACK_INVALID to STACK_MISC when allow_ptr_leaks is false, since invalid contents shouldn't be read unless the program has the relevant capabilities. The relaxation only makes sense when env->allow_ptr_leaks is true.
However, such conversion in privileged mode becomes unnecessary, as invalid slots can be read without being upgraded to STACK_MISC.
Currently, the condition is inverted (i.e. checking for true instead of false), simply remove it to restore correct behavior.
Fixes: eaf18febd6eb ("bpf: preserve STACK_ZERO slots on partial reg spills") Acked-by: Andrii Nakryiko andrii@kernel.org Reported-by: Tao Lyu tao.lyu@epfl.ch Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Link: https://lore.kernel.org/r/20241204044757.1483141-2-memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8955259112c03..cdf8ce1e2cc4f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1200,14 +1200,17 @@ static bool is_spilled_scalar_reg64(const struct bpf_stack_state *stack) /* Mark stack slot as STACK_MISC, unless it is already STACK_INVALID, in which * case they are equivalent, or it's STACK_ZERO, in which case we preserve * more precise STACK_ZERO. - * Note, in uprivileged mode leaving STACK_INVALID is wrong, so we take - * env->allow_ptr_leaks into account and force STACK_MISC, if necessary. + * Regardless of allow_ptr_leaks setting (i.e., privileged or unprivileged + * mode), we won't promote STACK_INVALID to STACK_MISC. In privileged case it is + * unnecessary as both are considered equivalent when loading data and pruning, + * in case of unprivileged mode it will be incorrect to allow reads of invalid + * slots. */ static void mark_stack_slot_misc(struct bpf_verifier_env *env, u8 *stype) { if (*stype == STACK_ZERO) return; - if (env->allow_ptr_leaks && *stype == STACK_INVALID) + if (*stype == STACK_INVALID) return; *stype = STACK_MISC; }