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Date: Sat, 27 Sep 2008 18:44:01 +0300
From: Avi Kivity <avi@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: viro@...IV.linux.org.uk, linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] ioctl: extensible ioctl dispatch
ioctls (as traditionally implemented) are very brittle; one cannot add
a field to the argument structure without breaking the ABI. In many
cases, this is a good thing as the ABI was not designed for extension.
In other cases, however, it makes sense to design an ABI with extension
in mind. This patch provides a new ioctl_dispatch_extensible(), which
is designed to cope with evolving interfaces:
- the ioctl number is matched only by its number and type, allowing
size and direction to change
- buffer space is allocated for the size the kernel expects, even if
the user passed a smaller buffer
- copying is limited by the size the kernel expects, even if the user
passed a larger buffer
- buffer size mismatches are handled by zeroing
The ABI can account for new fields either by recognizing zero as a "missing"
value, or by implementing bitflags for feature availability. Both an old
kernel with new userspace and a new kernel with old userspace are accomodated.
Signed-off-by: Avi Kivity <avi@...hat.com>
---
fs/ioctl.c | 87 +++++++++++++++++++++++++++++++++++++++++-------
include/linux/ioctl.h | 4 ++
2 files changed, 78 insertions(+), 13 deletions(-)
diff --git a/fs/ioctl.c b/fs/ioctl.c
index f63d5ce..5a354fc 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -225,12 +225,13 @@ asmlinkage long sys_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg)
* Locates and calls ioctl handler in @handlers; if none exist, calls
* @fallback; if that does not exist, return -ENOTTY.
*/
-long dispatch_ioctl(struct inode *inode, struct file *filp,
- unsigned cmd, unsigned long arg,
- const struct ioctl_handler *handlers,
- long (*fallback)(const struct ioctl_arg *arg))
+static long __dispatch_ioctl(struct inode *inode, struct file *filp,
+ unsigned cmd, unsigned long arg,
+ const struct ioctl_handler *handlers,
+ long (*fallback)(const struct ioctl_arg *arg),
+ unsigned cmd_mask)
{
- unsigned dir, size;
+ unsigned dir, size, usize, copysize;
long ret;
long stackbuf[IOCTL_STACK_BUF / sizeof(long)];
struct ioctl_arg iarg;
@@ -242,7 +243,7 @@ long dispatch_ioctl(struct inode *inode, struct file *filp,
* used (and performance sensitive) items are in the front.
*/
for (; handlers->handler; ++handlers)
- if (handlers->cmd == cmd) {
+ if ((handlers->cmd & cmd_mask) == (cmd & cmd_mask)) {
handler = handlers->handler;
break;
}
@@ -255,10 +256,14 @@ long dispatch_ioctl(struct inode *inode, struct file *filp,
iarg.inode = inode;
iarg.argl = arg;
- size = 0;
+ size = usize = 0;
dir = _IOC_DIR(cmd);
- if (dir != _IOC_NONE)
- size = _IOC_SIZE(cmd);
+ if (dir != _IOC_NONE) {
+ size = _IOC_SIZE(handlers->cmd);
+ usize = _IOC_SIZE(cmd);
+ if (!handlers->handler)
+ size = usize;
+ }
iarg.argp = stackbuf;
if (size > sizeof(stackbuf)) {
@@ -266,18 +271,28 @@ long dispatch_ioctl(struct inode *inode, struct file *filp,
if (!iarg.argp)
return -ENOMEM;
}
- if (dir & _IOC_WRITE)
- if (copy_from_user(iarg.argp, (void __user *)arg, size))
+
+ if (dir & _IOC_WRITE) {
+ copysize = min(size, usize);
+ if (copy_from_user(iarg.argp, (void __user *)arg, copysize))
goto out_fault;
+ if (copysize < size)
+ memset(iarg.argp + copysize, 0, size - copysize);
+ }
ret = handler(&iarg);
if (ret < 0)
goto out;
- if (dir & _IOC_READ)
- if (copy_to_user((void __user *)arg, iarg.argp, size))
+ if (dir & _IOC_READ) {
+ copysize = min(size, usize);
+ if (copy_to_user((void __user *)arg, iarg.argp, copysize))
goto out_fault;
+ for (; copysize < usize; ++copysize)
+ if (put_user(0, (u8 __user *)iarg.argp + copysize))
+ goto out_fault;
+ }
out:
if (iarg.argp != stackbuf)
kfree(iarg.argp);
@@ -288,4 +303,50 @@ out_fault:
ret = -EFAULT;
goto out;
}
+
+/**
+ * dispatch_ioctl - dispatch to an ioctl handler based on ioctl number
+ * @inode: inode to invoke ioctl method on
+ * @filp: open file to invoke ioctl method on
+ * @cmd: ioctl command to execute
+ * @arg: command-specific argument for ioctl
+ * @handlers: list of potential handlers for @cmd; null terminated;
+ * place frequently used cmds first
+ * @fallback: optional function to call if @cmd not found in @handlers
+ *
+ * Locates and calls ioctl handler in @handlers; if none exist, calls
+ * @fallback; if that does not exist, return -ENOTTY.
+ */
+long dispatch_ioctl(struct inode *inode, struct file *filp,
+ unsigned cmd, unsigned long arg,
+ const struct ioctl_handler *handlers,
+ long (*fallback)(const struct ioctl_arg *arg))
+{
+ return __dispatch_ioctl(inode, filp, cmd, arg, handlers, fallback, ~0);
+}
EXPORT_SYMBOL_GPL(dispatch_ioctl);
+
+/**
+ * dispatch_ioctl_extensible - dispatch to an ioctl handler based on ioctl
+ * number; adjust for differing buffer sizes
+ * between user and kernel
+ * @inode: inode to invoke ioctl method on
+ * @filp: open file to invoke ioctl method on
+ * @cmd: ioctl command to execute
+ * @arg: command-specific argument for ioctl
+ * @handlers: list of potential handlers for @cmd; null terminated;
+ * place frequently used cmds first
+ * @fallback: optional function to call if @cmd not found in @handlers
+ *
+ * Locates and calls ioctl handler in @handlers; if none exist, calls
+ * @fallback; if that does not exist, return -ENOTTY.
+ */
+long dispatch_ioctl_extensible(struct inode *inode, struct file *filp,
+ unsigned cmd, unsigned long arg,
+ const struct ioctl_handler *handlers,
+ long (*fallback)(const struct ioctl_arg *arg))
+{
+ return __dispatch_ioctl(inode, filp, cmd, arg, handlers, fallback,
+ ~(_IOC_SIZEMASK << _IOC_SIZESHIFT));
+}
+EXPORT_SYMBOL_GPL(dispatch_ioctl_extensible);
diff --git a/include/linux/ioctl.h b/include/linux/ioctl.h
index 881974a..5e73fbf 100644
--- a/include/linux/ioctl.h
+++ b/include/linux/ioctl.h
@@ -33,6 +33,10 @@ long dispatch_ioctl(struct inode *inode, struct file *filp,
unsigned int cmd, unsigned long arg,
const struct ioctl_handler *handlers,
long (*fallback)(const struct ioctl_arg *arg));
+long dispatch_ioctl_extensible(struct inode *inode, struct file *filp,
+ unsigned int cmd, unsigned long arg,
+ const struct ioctl_handler *handlers,
+ long (*fallback)(const struct ioctl_arg *arg));
#endif
--
1.6.0.1
--
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