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From: Sasha Levin <Alexander.Levin@microsoft.com>
To: "stable@vger.kernel.org" <stable@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: Jann Horn <jannh@google.com>,
	Boris Brezillon <boris.brezillon@bootlin.com>,
	Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 3.18 03/11] mtdchar: fix overflows in adjustment of `count`
Date: Sat, 15 Sep 2018 01:35:26 +0000	[thread overview]
Message-ID: <20180915013521.180178-3-alexander.levin@microsoft.com> (raw)
In-Reply-To: <20180915013521.180178-1-alexander.levin@microsoft.com>

From: Jann Horn <jannh@google.com>

[ Upstream commit 6c6bc9ea84d0008024606bf5ba10519e20d851bf ]

The first checks in mtdchar_read() and mtdchar_write() attempt to limit
`count` such that `*ppos + count <= mtd->size`. However, they ignore the
possibility of `*ppos > mtd->size`, allowing the calculation of `count` to
wrap around. `mtdchar_lseek()` prevents seeking beyond mtd->size, but the
pread/pwrite syscalls bypass this.

I haven't found any codepath on which this actually causes dangerous
behavior, but it seems like a sensible change anyway.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 drivers/mtd/mtdchar.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index 53563955931b..77f8f598344b 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -190,8 +190,12 @@ static ssize_t mtdchar_read(struct file *file, char __user *buf, size_t count,
 
 	pr_debug("MTD_read\n");
 
-	if (*ppos + count > mtd->size)
-		count = mtd->size - *ppos;
+	if (*ppos + count > mtd->size) {
+		if (*ppos < mtd->size)
+			count = mtd->size - *ppos;
+		else
+			count = 0;
+	}
 
 	if (!count)
 		return 0;
@@ -276,7 +280,7 @@ static ssize_t mtdchar_write(struct file *file, const char __user *buf, size_t c
 
 	pr_debug("MTD_write\n");
 
-	if (*ppos == mtd->size)
+	if (*ppos >= mtd->size)
 		return -ENOSPC;
 
 	if (*ppos + count > mtd->size)
-- 
2.17.1

  parent reply	other threads:[~2018-09-15  1:35 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-15  1:35 [PATCH AUTOSEL 3.18 01/11] binfmt_elf: Respect error return from `regset->active' Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 02/11] audit: fix use-after-free in audit_add_watch Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 04/11] MIPS: loongson64: cs5536: Fix PCI_OHCI_INT_REG reads Sasha Levin
2018-09-15  1:35 ` Sasha Levin [this message]
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 05/11] ARM: hisi: handle of_iomap and fix missing of_node_put Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 06/11] ARM: hisi: check " Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 07/11] parport: sunbpp: fix error return code Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 08/11] rtc: bq4802: add error handling for devm_ioremap Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 09/11] ALSA: pcm: Fix snd_interval_refine first/last with open min/max Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 10/11] drm/panel: type promotion bug in s6e8aa0_read_mtp_id() Sasha Levin
2018-09-15  1:35 ` [PATCH AUTOSEL 3.18 11/11] IB/nes: Fix a compiler warning Sasha Levin

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