6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nicholas Dudar [ Upstream commit 2aaf67f0516fde29620d0edfc29c01b9ea7ad430 ] check_kfunc_args() detects a kfunc argument named rdonly_buf_size or rdwr_buf_size and stores reg->var_off.value into meta->r0_size, a u64, and does not bound it. check_kfunc_call() later copies that value into the returned register's mem_size field: meta->r0_size = reg->var_off.value; ... regs[BPF_REG_0].mem_size = meta.r0_size; regs[BPF_REG_0].mem_size is u32. A constant whose upper 32 bits are set gets truncated instead of causing a load-time rejection, so the verifier records a PTR_TO_MEM register with an approximately 4 GiB mem_size for whatever allocation the kfunc returned. A later access check against that register uses the truncated, wrong bound. Reject rdonly_buf_size/rdwr_buf_size values that exceed U32_MAX at the point meta->r0_size is set. Fixes: eb1f7f71c126 ("bpf/verifier: allow kfunc to return an allocated mem") Signed-off-by: Nicholas Dudar Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260709155837.1879230-2-main.kalliope@gmail.com Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Kumar Kartikeya Dwivedi Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ac801a81f1967..6437863ff24c7 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11493,6 +11493,10 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ } meta->r0_size = reg->var_off.value; + if (meta->r0_size > U32_MAX) { + verbose(env, "R%d rdonly/rdwr_buf_size exceeds u32 max\n", regno); + return -EINVAL; + } ret = mark_chain_precision(env, regno); if (ret) return ret; -- 2.53.0