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: fa28dcb ("bpf: Introduce helper bpf_get_task_stack()") Cc: [email protected] # v5.9+ Signed-off-by: Naveen N. Rao <[email protected]> Acked-by: Daniel Borkmann <[email protected]> Signed-off-by: Michael Ellerman <[email protected]> Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@linux.vnet.ibm.com
sm00th · Jan 15, 2022 · b992f01 · b992f01
1 parent 29ec39f
commit b992f01
Showing 1 changed file with 3 additions and 2 deletions.
diff --git 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;