[PATCH v3 2/2] ARM: mm: protect show_pte() in do_DataAbort() fallback path

[Qi Xi]

The do_DataAbort() fallback path handles FSR types not serviced by
do_page_fault() (fsr_info entries with fn=do_bad). This path also
calls show_pte() without holding mmap_read_lock, exposing it to
the same use-after-free issue.

Since do_DataAbort() is an exception entry point that can be reached
from contexts where sleeping is not allowed, use mmap_read_trylock().
If the lock cannot be acquired, the page table dump is skipped.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Suggested-by: Yuanbin Xie <xieyuanbin1 at huawei.com>
Signed-off-by: Qi Xi <xiqi2 at huawei.com>
---
 arch/arm/mm/fault.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 1f2a85e1fa..0a8fc40afe 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -638,7 +638,10 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	pr_alert("8<--- cut here ---\n");
 	pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
 		inf->name, fsr, addr);
-	show_pte(KERN_ALERT, current->mm, addr);
+	if (mmap_read_trylock(current->mm)) {
+		show_pte(KERN_ALERT, current->mm, addr);
+		mmap_read_unlock(current->mm);
+	}
 
 	arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
 		       fsr, 0);
-- 
2.33.0