linux-kernel - [PATCH v2] fuse: Fix IOC_[GS]ET{FLAGS,VERSION} argument size brokenness.

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Message-ID: <20131220233534.GC10192@birch.djwong.org>
Date:	Fri, 20 Dec 2013 15:35:34 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Miklos Szeredi <miklos@...redi.hu>,
	Alexander Viro <viro@...iv.linux.org.uk>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	fuse-devel@...ts.sourceforge.net,
	Richard Hansen <rhansen@...nsen.org>
Subject: [PATCH v2] fuse: Fix IOC_[GS]ET{FLAGS,VERSION} argument size
 brokenness.

The IOC_[GS]ETFLAGS and IOC_[GS]ETVERSION ioctls, despite being
defined to take a "long" parameter, actually take "int" parameters.
FUSE unfortunately assumed that the ioctl definitions never lie, and
transfers a long's worth of data in and out of userspace, which causes
stack smashing in chattr, and other bugs elsewhere.

So, special-case this in FUSE so that we don't crash userland.

v2: Do the same for the IOC_[GS]ETVERSION ioctls, as Richard Hansen
    points out.

Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
---
 fs/fuse/file.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 7e70506..f8766ab 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2385,6 +2385,22 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 		iov->iov_base = (void __user *)arg;
 		iov->iov_len = _IOC_SIZE(cmd);
 
+		/*
+		 * The IOC_[GS]ETFLAGS and IOC_[GS]ETVERSION ioctls take int
+		 * parameters even though the ioctl definition specifies long.
+		 * Userland has been expecting int for ages (and chattr
+		 * segfaults on FUSE filesystems), so special case that here.
+		 * The IOC32 variants were declared with int, so they don't
+		 * need this correction.
+		 */
+		switch (cmd) {
+		case FS_IOC_GETFLAGS:
+		case FS_IOC_SETFLAGS:
+		case FS_IOC_GETVERSION:
+		case FS_IOC_SETVERSION:
+			iov->iov_len = sizeof(int);
+		}
+
 		if (_IOC_DIR(cmd) & _IOC_WRITE) {
 			in_iov = iov;
 			in_iovs = 1;
--
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