Commit b992f01e authored by Naveen N. Rao's avatar Naveen N. Rao Committed by Michael Ellerman
Browse files

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: fa28dcb8 ("bpf: Introduce helper bpf_get_task_stack()")
Cc: stable@vger.kernel.org # v5.9+
Signed-off-by: default avatarNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@linux.vnet.ibm.com
parent 29ec39fc

kernel/bpf/stackmap.c

+3 −2
Original line number Diff line number Diff line
@@ -472,12 +472,13 @@ 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);

	if (regs)

		res = __bpf_get_stack(regs, task, NULL, buf, size, flags);

	put_task_stack(task);