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bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack()

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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: fa28dcb82a ("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
This commit is contained in:
Naveen N. Rao 2022-01-06 17:15:05 +05:30 committed by Michael Ellerman
parent 29ec39fcf1
commit b992f01e66
1 changed files with 3 additions and 2 deletions
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5
kernel/bpf/stackmap.c
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@ -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;