[PATCH] memcg: Check more strictly to avoid ULLONG overflow by PAGE_ALIGN

[Sha Zhengju <handai.szj@gmail.com>]

From: Sha Zhengju <handai.szj@taobao.com>

While writing memory.limit_in_bytes, a confusing result may happen:

$ mkdir /memcg/test
$ cat /memcg/test/memory.limit_in_bytes
9223372036854775807
$ cat /memcg/test/memory.memsw.limit_in_bytes
9223372036854775807
$ echo 18446744073709551614 > /memcg/test/memory.limit_in_bytes
$ cat /memcg/test/memory.limit_in_bytes
0

Strangely, the write successed and reset the limit to 0.
The patch corrects RESOURCE_MAX and fixes this kind of overflow.


Signed-off-by: Sha Zhengju <handai.szj@taobao.com>
Reported-by: Li Wenpeng < xingke.lwp@taobao.com>
Cc: Jie Liu <jeff.liu@oracle.com>
---
 include/linux/res_counter.h |    2 +-
 kernel/res_counter.c        |    8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
index c230994..c2f01fc 100644
--- a/include/linux/res_counter.h
+++ b/include/linux/res_counter.h
@@ -54,7 +54,7 @@ struct res_counter {
 	struct res_counter *parent;
 };
 
-#define RESOURCE_MAX (unsigned long long)LLONG_MAX
+#define RESOURCE_MAX (unsigned long long)ULLONG_MAX
 
 /**
  * Helpers to interact with userspace
diff --git a/kernel/res_counter.c b/kernel/res_counter.c
index ff55247..6c35310 100644
--- a/kernel/res_counter.c
+++ b/kernel/res_counter.c
@@ -195,6 +195,12 @@ int res_counter_memparse_write_strategy(const char *buf,
 	if (*end != '\0')
 		return -EINVAL;
 
-	*res = PAGE_ALIGN(*res);
+	/* Since PAGE_ALIGN is aligning up(the next page boundary),
+	 * check the left space to avoid overflow to 0. */
+	if (RESOURCE_MAX - *res < PAGE_SIZE - 1)
+		*res = RESOURCE_MAX;
+	else
+		*res = PAGE_ALIGN(*res);
+
 	return 0;
 }
-- 
1.7.9.5

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