linux-kernel - [PATCH 1/2] proc: fix inode number bogorithmetic

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Message-ID: <20080726071828.GA5115@martell.zuzino.mipt.ru>
Date:	Sat, 26 Jul 2008 11:18:28 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	akpm@...l.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] proc: fix inode number bogorithmetic

Id which proc gets from IDR for inode number and id which proc removes
from IDR do not match. E.g. 0x11a transforms into 0x8000011a.

Which stayed unnoticed for a long time because, surprise, idr_remove()
masks out that high bit before doing anything.

All of this due to "| ~MAX_ID_MASK" in release_inode_number().

I still don't understand how it's supposed to work, because "| ~MASK"
is not an inversion for "& MAX" operation.

So, use just one nice, working addition. Make start offset unsigned int,
while I'm at it. It's longness is not used anywhere.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/generic.c |   21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -303,7 +303,7 @@ out:
 static DEFINE_IDR(proc_inum_idr);
 static DEFINE_SPINLOCK(proc_inum_lock); /* protects the above */
 
-#define PROC_DYNAMIC_FIRST 0xF0000000UL
+#define PROC_DYNAMIC_FIRST 0xF0000000U
 
 /*
  * Return an inode number between PROC_DYNAMIC_FIRST and
@@ -311,7 +311,7 @@ static DEFINE_SPINLOCK(proc_inum_lock); /* protects the above */
  */
 static unsigned int get_inode_number(void)
 {
-	int i, inum = 0;
+	unsigned int i;
 	int error;
 
 retry:
@@ -326,21 +326,18 @@ retry:
 	else if (error)
 		return 0;
 
-	inum = (i & MAX_ID_MASK) + PROC_DYNAMIC_FIRST;
-
-	/* inum will never be more than 0xf0ffffff, so no check
-	 * for overflow.
-	 */
-
-	return inum;
+	if (i > UINT_MAX - PROC_DYNAMIC_FIRST) {
+		spin_lock(&proc_inum_lock);
+		idr_remove(&proc_inum_idr, i);
+		spin_unlock(&proc_inum_lock);
+	}
+	return PROC_DYNAMIC_FIRST + i;
 }
 
 static void release_inode_number(unsigned int inum)
 {
-	int id = (inum - PROC_DYNAMIC_FIRST) | ~MAX_ID_MASK;
-
 	spin_lock(&proc_inum_lock);
-	idr_remove(&proc_inum_idr, id);
+	idr_remove(&proc_inum_idr, inum - PROC_DYNAMIC_FIRST);
 	spin_unlock(&proc_inum_lock);
 }
 
-- 
1.5.4.5


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