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Subject[PATCH 5.10 007/100] bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack()
Date
From: Naveen N. Rao <naveen.n.rao@linux.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@vger.kernel.org # v5.9+
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.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@linuxfoundation.org>
---
kernel/bpf/stackmap.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -664,13 +664,14 @@ 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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