[140/212] mm/vmalloc: fix wrong behavior in vread

Commit Message

Andrew Morton Sept. 2, 2021, 9:57 p.m. UTC

From: Chen Wandun <[e-mail]>
Subject: 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/[e-mail]
Fixes: f608788cd2d6 ("mm/vmalloc: use rb_tree instead of list for vread() lookups")
Signed-off-by: Chen Wandun <[e-mail]>
Reported-by: Hulk Robot <[e-mail]>
Cc: Serapheim Dimitropoulos <[e-mail]>
Cc: Uladzislau Rezki (Sony) <[e-mail]>
Cc: Kefeng Wang <[e-mail]>
Cc: Wei Yongjun <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/vmalloc.c |   29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

Patch

--- a/mm/vmalloc.c~mm-vmalloc-fix-wrong-behavior-in-vread
+++ a/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, unsign
 		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;