linux-kernel - [PATCH 1/5] lib: make bitmap_parselist_user() a wrapper on bitmap

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Message-Id: <20190403044540.16322-2-ynorov@marvell.com>
Date:   Wed,  3 Apr 2019 07:45:36 +0300
From:   Yury Norov <yury.norov@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Mike Travis <travis@....com>
Cc:     Yury Norov <ynorov@...vell.com>, Yury Norov <yury.norov@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/5] lib: make bitmap_parselist_user() a wrapper on bitmap_parselist()

Currently we parse user data byte after byte which leads to
overcomplification of parsing algorithm. The only user of
bitmap_parselist_user() is not performance-critical, and so we
can copy user data to kernel buffer and simply call
bitmap_parselist(). This rework lets us unify and simplify
bitmap_parselist() and bitmap_parselist_user(), which is done
in the following patch.

Signed-off-by: Yury Norov <ynorov@...vell.com>
---
 lib/bitmap.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 98872e9025da..ce9ea804d06d 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -632,19 +632,30 @@ EXPORT_SYMBOL(bitmap_parselist);
  * @nmaskbits: size of bitmap, in bits.
  *
  * Wrapper for bitmap_parselist(), providing it with user buffer.
- *
- * We cannot have this as an inline function in bitmap.h because it needs
- * linux/uaccess.h to get the access_ok() declaration and this causes
- * cyclic dependencies.
  */
 int bitmap_parselist_user(const char __user *ubuf,
 			unsigned int ulen, unsigned long *maskp,
 			int nmaskbits)
 {
-	if (!access_ok(ubuf, ulen))
-		return -EFAULT;
-	return __bitmap_parselist((const char __force *)ubuf,
-					ulen, 1, maskp, nmaskbits);
+	char *buf;
+	int ret;
+
+	buf = kmalloc(ulen + 1, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	buf[ulen] = 0;
+
+	ret = copy_from_user(buf, ubuf, ulen);
+	if (ret)
+		goto out;
+
+	ret = bitmap_parselist(buf, maskp, nmaskbits);
+
+out:
+	kfree(buf);
+
+	return ret;
 }
 EXPORT_SYMBOL(bitmap_parselist_user);
 
-- 
2.17.1