From b992f01e66150fc5e90be4a96f5eb8e634c8249e Mon Sep 17 00:00:00 2001 From: "Naveen N. Rao" Date: Thu, 6 Jan 2022 17:15:05 +0530 Subject: [PATCH] bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack() task_pt_regs() can return NULL on powerpc for kernel threads. This is then used in __bpf_get_stack() to check for user mode, resulting in a kernel oops. Guard against this by checking return value of task_pt_regs() before trying to obtain the call chain. Fixes: fa28dcb82a38f8 ("bpf: Introduce helper bpf_get_task_stack()") Cc: stable@vger.kernel.org # v5.9+ Signed-off-by: Naveen N. Rao Acked-by: Daniel Borkmann Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@linux.vnet.ibm.com --- kernel/bpf/stackmap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 49e567209c6b..22c8ae94e4c1 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -472,13 +472,14 @@ BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf, u32, size, u64, flags) { struct pt_regs *regs; - long res; + long res = -EINVAL; if (!try_get_task_stack(task)) return -EFAULT; regs = task_pt_regs(task); - res = __bpf_get_stack(regs, task, NULL, buf, size, flags); + if (regs) + res = __bpf_get_stack(regs, task, NULL, buf, size, flags); put_task_stack(task); return res;