ARM: Ensure do_cache_op takes mmap_sem

do_cache_op() uses find_vma() to validate its arguments without holding
any locking.  This means that the VMA could vanish beneath us.  Fix
this by taking a read lock on mmap_sem.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 57eb0f6f6005..467b69ed1021 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -418,12 +418,14 @@ static int bad_syscall(int n, struct pt_regs *regs)
 static inline void
 do_cache_op(unsigned long start, unsigned long end, int flags)
 {
+        struct mm_struct *mm = current->active_mm;
         struct vm_area_struct *vma;
 
         if (end < start || flags)
                 return;
 
-        vma = find_vma(current->active_mm, start);
+        down_read(&mm->mmap_sem);
+        vma = find_vma(mm, start);
         if (vma && vma->vm_start < end) {
                 if (start < vma->vm_start)
                         start = vma->vm_start;
@@ -432,6 +434,7 @@ do_cache_op(unsigned long start, unsigned long end, int flags)
 
                 flush_cache_user_range(vma, start, end);
         }
+        up_read(&mm->mmap_sem);
 }
 
 /*