From: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx # v5.9+
Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@xxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
