linux-kernel - [PATCH upstream] KASAN: slab-out-of-bounds Read in getname

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Date:   Mon, 2 Jul 2018 00:04:10 +0200
From:   tomas <tomasbortoli@...il.com>
To:     raven@...maw.net, autofs@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, syzkaller@...glegroups.com
Subject: [PATCH upstream] KASAN: slab-out-of-bounds Read in getname_kernel

Hi,

I've looked into this issue found by Syzbot and I made a patch:

https://syzkaller.appspot.com/bug?id=d03abd8b42847f7f69b1d1d7f97208ae425b1163

The autofs subsystem does not check that the "path" parameter is present
within the "param" struct passed by the userspace in case the
AUTOFS_DEV_IOCTL_OPENMOUNT_CMD command is passed. Indeed, it assumes a
path is always provided (though a path is not always present, as per how
the struct is defined:
https://github.com/torvalds/linux/blob/master/include/uapi/linux/auto_dev-ioctl.h#L89).
Skipping the check provokes an oob read in "strlen", called by
"getname_kernel", in turn called by the autofs to assess the length of
the non-existing path.

To solve it, modify the "validate_dev_ioctl" function to check also that
a path has been provided if the command is AUTOFS_DEV_IOCTL_OPENMOUNT_CMD.

--- b/fs/autofs/dev-ioctl.c    2018-07-01 23:10:16.059728621 +0200
+++ a/fs/autofs/dev-ioctl.c    2018-07-01 23:10:24.311792133 +0200
@@ -136,6 +136,9 @@ static int validate_dev_ioctl(int cmd, s
             goto out;
         }
     }
+    /* AUTOFS_DEV_IOCTL_OPENMOUNT_CMD without path */
+    else if(_IOC_NR(cmd) == AUTOFS_DEV_IOCTL_OPENMOUNT_CMD)
+        return -EINVAL;

     err = 0;
 out:

Tested and solves the issue on Linus' main git tree.

Tomas