m68k: sun3: add check for __pgd_alloc()

Add check for the return value of __pgd_alloc() in pgd_alloc() to prevent
null pointer dereference.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: a9b3c35 ("asm-generic: pgalloc: provide generic __pgd_{alloc,free}")
Signed-off-by: Haoxiang Li <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Kevin Brodsky <[email protected]>
Cc: Qi Zheng <[email protected]>
Cc: Sam Creasey <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Haoxiang Li

arch/m68k/include/asm/sun3_pgalloc.h

@@ -44,8 +44,10 @@ static inline pgd_t * pgd_alloc(struct mm_struct *mm)
 	pgd_t *new_pgd;
 
 	new_pgd = __pgd_alloc(mm, 0);
-	memcpy(new_pgd, swapper_pg_dir, PAGE_SIZE);
-	memset(new_pgd, 0, (PAGE_OFFSET >> PGDIR_SHIFT));
+	if (likely(new_pgd != NULL)) {
+		memcpy(new_pgd, swapper_pg_dir, PAGE_SIZE);
+		memset(new_pgd, 0, (PAGE_OFFSET >> PGDIR_SHIFT));
+	}
 	return new_pgd;
 }