[PATCH 4.17 072/101] autofs: fix slab out of bounds read in getname_kernel()

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tomas Bortoli <tomasbortoli@xxxxxxxxx>

commit 02f51d45937f7bc7f4dee21e9f85b2d5eac37104 upstream.

The autofs subsystem does not check that the "path" parameter is present
for all cases where it is required when it is passed in via the "param"
struct.

In particular it isn't checked for the AUTOFS_DEV_IOCTL_OPENMOUNT_CMD
ioctl command.

To solve it, modify validate_dev_ioctl(function to check that a path has
been provided for ioctl commands that require it.

Link: http://lkml.kernel.org/r/153060031527.26631.18306637892746301555.stgit@xxxxxxxxxxxxxxxx
Signed-off-by: Tomas Bortoli <tomasbortoli@xxxxxxxxx>
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Reported-by: syzbot+60c837b428dc84e83a93@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/autofs4/dev-ioctl.c |   22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -148,6 +148,15 @@ static int validate_dev_ioctl(int cmd, s
 				cmd);
 			goto out;
 		}
+	} else {
+		unsigned int inr = _IOC_NR(cmd);
+
+		if (inr == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD ||
+		    inr == AUTOFS_DEV_IOCTL_REQUESTER_CMD ||
+		    inr == AUTOFS_DEV_IOCTL_ISMOUNTPOINT_CMD) {
+			err = -EINVAL;
+			goto out;
+		}
 	}
 
 	err = 0;
@@ -284,7 +293,8 @@ static int autofs_dev_ioctl_openmount(st
 	dev_t devid;
 	int err, fd;
 
-	/* param->path has already been checked */
+	/* param->path has been checked in validate_dev_ioctl() */
+
 	if (!param->openmount.devid)
 		return -EINVAL;
 
@@ -446,10 +456,7 @@ static int autofs_dev_ioctl_requester(st
 	dev_t devid;
 	int err = -ENOENT;
 
-	if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
-		err = -EINVAL;
-		goto out;
-	}
+	/* param->path has been checked in validate_dev_ioctl() */
 
 	devid = sbi->sb->s_dev;
 
@@ -534,10 +541,7 @@ static int autofs_dev_ioctl_ismountpoint
 	unsigned int devid, magic;
 	int err = -ENOENT;
 
-	if (param->size <= AUTOFS_DEV_IOCTL_SIZE) {
-		err = -EINVAL;
-		goto out;
-	}
+	/* param->path has been checked in validate_dev_ioctl() */
 
 	name = param->path;
 	type = param->ismountpoint.in.type;