linux-kernel - [PATCH] UBI: Don't use signed int as array index before testing if it is negative

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Message-Id: <200708040125.26861.jesper.juhl@gmail.com>
Date:	Sat, 4 Aug 2007 01:25:26 +0200
From:	Jesper Juhl <jesper.juhl@...il.com>
To:	Artem Bityutskiy <dedekind@...radead.org>
Cc:	linux-mtd@...ts.infradead.org,
	David Woodhouse <dwmw2@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesper Juhl <jesper.juhl@...il.com>
Subject: [PATCH] UBI: Don't use signed int as array index before testing if it is negative

Hi,

I can't find anything guaranteeing that 'ubi_num' cannot be <0 in 
drivers/mtd/ubi/kapi.c::ubi_open_volume(), and in fact the code 
even tests for that and errors out if so. Unfortunately the test 
for "ubi_num < 0" happens after we've already used 'ubi_num' as 
an array index - bad thing to do if it is negative.
This patch moves the test earlier in the function and then moves 
the indexing using that variable after the check. A bit safer :-) 


Signed-off-by: Jesper Juhl <jesper.juhl@...il.com>
---

 drivers/mtd/ubi/kapi.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
index 4a458e8..5130e54 100644
--- a/drivers/mtd/ubi/kapi.c
+++ b/drivers/mtd/ubi/kapi.c
@@ -99,16 +99,21 @@ struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode)
 {
 	int err;
 	struct ubi_volume_desc *desc;
-	struct ubi_device *ubi = ubi_devices[ubi_num];
+	struct ubi_device *ubi;
 	struct ubi_volume *vol;
 
 	dbg_msg("open device %d volume %d, mode %d", ubi_num, vol_id, mode);
 
 	err = -ENODEV;
+	if (ubi_num < 0)
+		return ERR_PTR(err);
+
+	ubi = ubi_devices[ubi_num];
+	
 	if (!try_module_get(THIS_MODULE))
 		return ERR_PTR(err);
 
-	if (ubi_num < 0 || ubi_num >= UBI_MAX_DEVICES || !ubi)
+	if (ubi_num >= UBI_MAX_DEVICES || !ubi)
 		goto out_put;
 
 	err = -EINVAL;


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