[PATCH 5.15 34/83] mm,hwpoison: check mm when killing accessing process

[Greg Kroah-Hartman]

From: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>

commit 77677cdbc2aa4b5d5d839562793d3d126201d18d upstream.

The GHES code calls memory_failure_queue() from IRQ context to queue work
into workqueue and schedule it on the current CPU.  Then the work is
processed in memory_failure_work_func() by kworker and calls
memory_failure().

When a page is already poisoned, commit a3f5d80ea401 ("mm,hwpoison: send
SIGBUS with error virutal address") make memory_failure() call
kill_accessing_process() that:

    - holds mmap locking of current->mm
    - does pagetable walk to find the error virtual address
    - and sends SIGBUS to the current process with error info.

However, the mm of kworker is not valid, resulting in a null-pointer
dereference.  So check mm when killing the accessing process.

[akpm@xxxxxxxxxxxxxxxxxxxx: remove unrelated whitespace alteration]
Link: https://lkml.kernel.org/r/20220914064935.7851-1-xueshuai@xxxxxxxxxxxxxxxxx
Fixes: a3f5d80ea401 ("mm,hwpoison: send SIGBUS with error virutal address")
Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/memory-failure.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -700,6 +700,9 @@ static int kill_accessing_process(struct
 	};
 	priv.tk.tsk = p;
 
+	if (!p->mm)
+		return -EFAULT;
+
 	mmap_read_lock(p->mm);
 	ret = walk_page_range(p->mm, 0, TASK_SIZE, &hwp_walk_ops,
 			      (void *)&priv);