linux-kernel - [PATCH] resource: fix an error which walks through iomem resources

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Message-Id: <20180917062029.511-1-lijiang@redhat.com>
Date:   Mon, 17 Sep 2018 14:20:29 +0800
From:   Lianbo Jiang <lijiang@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     dan.j.williams@...el.com, thomas.lendacky@....com,
        akpm@...ux-foundation.org, tglx@...utronix.de, bhelgaas@...gle.com,
        baiyaowei@...s.chinamobile.com, tiwai@...e.de, bp@...e.de,
        brijesh.singh@....com, dyoung@...hat.com
Subject: [PATCH] resource: fix an error which walks through iomem resources

When we walk through iomem resources by calling walk_iomem_res_desc(), the
values of the function parameter may be modified in the while loop of __walk
_iomem_res_desc(), which will cause us to not get the desired result in some
cases.

At present, it only restores the original value of res->end, but it doesn't
restore the original value of res->flags in the while loop of __walk_iomem
_res_desc(). Whenever the find_next_iomem_res() finds a resource and returns
the result, the original values of this resource will be modified, which might
lead to an error in the next loop. For example:

The original value of resource flags is: res->flags=0x80000200(initial value)

p->flags   _ 0x81000200 _                _ 0x80000200 _
          /              \              /              \
|________|_______A________|____|_....._|______B_________|......___|
0                                                                 0xffffffff
                (memory address ranges)

Note: if ((p->flags & res->flags) != res->flags) continue;

When the resource A is found, the original value of this resource flags will
be changed to 0x81000200(res->flags=0x81000200), and continue to look for the
next resource, when the loop reaches resource B, it can not get the resource B
any more(you can refer to the for loop of find_next_iomem_res()), because the
value of conditional expression will become true and will also jump the resource
B. In fact, we should get the resource A and B when we walk through the whole
tree, but it only gets the resource A, the resource B is missed.

Signed-off-by: Lianbo Jiang <lijiang@...hat.com>
---
 kernel/resource.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/resource.c b/kernel/resource.c
index 30e1bc68503b..f5d9fc70a04c 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -375,6 +375,7 @@ static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,
 				 int (*func)(struct resource *, void *))
 {
 	u64 orig_end = res->end;
+	u64 orig_flags = res->flags;
 	int ret = -1;

 	while ((res->start < res->end) &&
@@ -385,6 +386,7 @@ static int __walk_iomem_res_desc(struct resource *res, unsigned long desc,

 		res->start = res->end + 1;
 		res->end = orig_end;
+		res->flags = orig_flags;
 	}

 	return ret;
-- 
2.17.1