mm/vmalloc: fix wrong behavior in vread

commit f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread()
lookups") use rb_tree instread of list to speed up lookup, but function
__find_vmap_area is try to find a vmap_area that include target address,
if target address is smaller than the leftmost node in vmap_area_root, it
will return NULL, then vread will read nothing.  This behavior is
different from the primitive semantics.

The correct way is find the first vmap_are that bigger than target addr,
that is what function find_vmap_area_exceed_addr does.

Link: https://lkml.kernel.org/r/20210714015959.3204871-1-chenwandun@huawei.com
Fixes: f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread() lookups")
Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Cc: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 5dcb65d..3824dc1 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -787,6 +787,28 @@ unsigned long vmalloc_nr_pages(void)
        return atomic_long_read(&nr_vmalloc_pages);
 }
 
+static struct vmap_area *find_vmap_area_exceed_addr(unsigned long addr)
+{
+       struct vmap_area *va = NULL;
+       struct rb_node *n = vmap_area_root.rb_node;
+
+       while (n) {
+               struct vmap_area *tmp;
+
+               tmp = rb_entry(n, struct vmap_area, rb_node);
+               if (tmp->va_end > addr) {
+                       va = tmp;
+                       if (tmp->va_start <= addr)
+                               break;
+
+                       n = n->rb_left;
+               } else
+                       n = n->rb_right;
+       }
+
+       return va;
+}
+
 static struct vmap_area *__find_vmap_area(unsigned long addr)
 {
        struct rb_node *n = vmap_area_root.rb_node;
@@ -3287,9 +3309,14 @@ long vread(char *buf, char *addr, unsigned long count)
                count = -(unsigned long) addr;
 
        spin_lock(&vmap_area_lock);
-       va = __find_vmap_area((unsigned long)addr);
+       va = find_vmap_area_exceed_addr((unsigned long)addr);
        if (!va)
                goto finished;
+
+       /* no intersects with alive vmap_area */
+       if ((unsigned long)addr + count <= va->va_start)
+               goto finished;
+
        list_for_each_entry_from(va, &vmap_area_list, list) {
                if (!count)
                        break;