linux-kernel - [PATCH 5.2 382/413] resource: fix locking in find_next_iomem

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Date:   Wed, 24 Jul 2019 21:21:13 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Nadav Amit <namit@...are.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Borislav Petkov <bp@...e.de>, Toshi Kani <toshi.kani@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.2 382/413] resource: fix locking in find_next_iomem_res()

From: Nadav Amit <namit@...are.com>

commit 49f17c26c123b60fd1c74629eef077740d16ffc2 upstream.

Since resources can be removed, locking should ensure that the resource
is not removed while accessing it.  However, find_next_iomem_res() does
not hold the lock while copying the data of the resource.

Keep holding the lock while the data is copied.  While at it, change the
return value to a more informative value.  It is disregarded by the
callers.

[akpm@...ux-foundation.org: fix find_next_iomem_res() documentation]
Link: http://lkml.kernel.org/r/20190613045903.4922-2-namit@vmware.com
Fixes: ff3cc952d3f00 ("resource: Add remove_resource interface")
Signed-off-by: Nadav Amit <namit@...are.com>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Reviewed-by: Dan Williams <dan.j.williams@...el.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Toshi Kani <toshi.kani@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/resource.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -326,7 +326,7 @@ EXPORT_SYMBOL(release_resource);
  *
  * If a resource is found, returns 0 and @*res is overwritten with the part
  * of the resource that's within [@start..@end]; if none is found, returns
- * -1 or -EINVAL for other invalid parameters.
+ * -ENODEV.  Returns -EINVAL for invalid parameters.
  *
  * This function walks the whole tree and not just first level children
  * unless @first_lvl is true.
@@ -365,16 +365,16 @@ static int find_next_iomem_res(resource_
 			break;
 	}
 
-	read_unlock(&resource_lock);
-	if (!p)
-		return -1;
+	if (p) {
+		/* copy data */
+		res->start = max(start, p->start);
+		res->end = min(end, p->end);
+		res->flags = p->flags;
+		res->desc = p->desc;
+	}
 
-	/* copy data */
-	res->start = max(start, p->start);
-	res->end = min(end, p->end);
-	res->flags = p->flags;
-	res->desc = p->desc;
-	return 0;
+	read_unlock(&resource_lock);
+	return p ? 0 : -ENODEV;
 }
 
 static int __walk_iomem_res_desc(resource_size_t start, resource_size_t end,