[dm-devel] Patch "dm ioctl: Avoid double-fetch of version" has been added to the 6.1-stable tree

[dm-devel] Patch "dm ioctl: Avoid double-fetch of version" has been added to the 6.1-stable tree

[Sasha Levin]

This is a note to let you know that I've just added the patch titled

    dm ioctl: Avoid double-fetch of version

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dm-ioctl-avoid-double-fetch-of-version.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.



commit edad1af6376d882614441fb3632a88a31e49a527
Author: Demi Marie Obenour <demi@invisiblethingslab.com>
Date:   Sat Jun 3 10:52:42 2023 -0400

    dm ioctl: Avoid double-fetch of version
    
    [ Upstream commit 249bed821b4db6d95a99160f7d6d236ea5fe6362 ]
    
    The version is fetched once in check_version(), which then does some
    validation and then overwrites the version in userspace with the API
    version supported by the kernel.  copy_params() then fetches the version
    from userspace *again*, and this time no validation is done.  The result
    is that the kernel's version number is completely controllable by
    userspace, provided that userspace can win a race condition.
    
    Fix this flaw by not copying the version back to the kernel the second
    time.  This is not exploitable as the version is not further used in the
    kernel.  However, it could become a problem if future patches start
    relying on the version field.
    
    Cc: stable@vger.kernel.org
    Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
    Signed-off-by: Mike Snitzer <snitzer@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 6aeae095086d7..2afd2d2a0f407 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1811,30 +1811,36 @@ static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
  * As well as checking the version compatibility this always
  * copies the kernel interface version out.
  */
-static int check_version(unsigned int cmd, struct dm_ioctl __user *user)
+static int check_version(unsigned int cmd, struct dm_ioctl __user *user,
+			 struct dm_ioctl *kernel_params)
 {
-	uint32_t version[3];
 	int r = 0;
 
-	if (copy_from_user(version, user->version, sizeof(version)))
+	/* Make certain version is first member of dm_ioctl struct */
+	BUILD_BUG_ON(offsetof(struct dm_ioctl, version) != 0);
+
+	if (copy_from_user(kernel_params->version, user->version, sizeof(kernel_params->version)))
 		return -EFAULT;
 
-	if ((version[0] != DM_VERSION_MAJOR) ||
-	    (version[1] > DM_VERSION_MINOR)) {
+	if ((kernel_params->version[0] != DM_VERSION_MAJOR) ||
+	    (kernel_params->version[1] > DM_VERSION_MINOR)) {
 		DMERR("ioctl interface mismatch: kernel(%u.%u.%u), user(%u.%u.%u), cmd(%d)",
 		      DM_VERSION_MAJOR, DM_VERSION_MINOR,
 		      DM_VERSION_PATCHLEVEL,
-		      version[0], version[1], version[2], cmd);
+		      kernel_params->version[0],
+		      kernel_params->version[1],
+		      kernel_params->version[2],
+		      cmd);
 		r = -EINVAL;
 	}
 
 	/*
 	 * Fill in the kernel version.
 	 */
-	version[0] = DM_VERSION_MAJOR;
-	version[1] = DM_VERSION_MINOR;
-	version[2] = DM_VERSION_PATCHLEVEL;
-	if (copy_to_user(user->version, version, sizeof(version)))
+	kernel_params->version[0] = DM_VERSION_MAJOR;
+	kernel_params->version[1] = DM_VERSION_MINOR;
+	kernel_params->version[2] = DM_VERSION_PATCHLEVEL;
+	if (copy_to_user(user->version, kernel_params->version, sizeof(kernel_params->version)))
 		return -EFAULT;
 
 	return r;
@@ -1860,7 +1866,10 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
 	const size_t minimum_data_size = offsetof(struct dm_ioctl, data);
 	unsigned int noio_flag;
 
-	if (copy_from_user(param_kernel, user, minimum_data_size))
+	/* check_version() already copied version from userspace, avoid TOCTOU */
+	if (copy_from_user((char *)param_kernel + sizeof(param_kernel->version),
+			   (char __user *)user + sizeof(param_kernel->version),
+			   minimum_data_size - sizeof(param_kernel->version)))
 		return -EFAULT;
 
 	if (param_kernel->data_size < minimum_data_size) {
@@ -1972,7 +1981,7 @@ static int ctl_ioctl(struct file *file, uint command, struct dm_ioctl __user *us
 	 * Check the interface version passed in.  This also
 	 * writes out the kernel's interface version.
 	 */
-	r = check_version(cmd, user);
+	r = check_version(cmd, user, &param_kernel);
 	if (r)
 		return r;
 

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