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Date: Mon, 31 Jan 2022 11:54:44 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>, Daniel Borkmann <daniel@...earbox.net>, Michael Ellerman <mpe@...erman.id.au> Subject: [PATCH 5.16 021/200] bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack() From: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com> commit b992f01e66150fc5e90be4a96f5eb8e634c8249e upstream. 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@...r.kernel.org # v5.9+ Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com> Acked-by: Daniel Borkmann <daniel@...earbox.net> Signed-off-by: Michael Ellerman <mpe@...erman.id.au> Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@linux.vnet.ibm.com Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- kernel/bpf/stackmap.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -525,13 +525,14 @@ BPF_CALL_4(bpf_get_task_stack, struct ta 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;
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