Hi, On Thu, Sep 15, 2011 at 13:14 +0400, Cyrill Gorcunov wrote: > On Wed, Sep 14, 2011 at 08:07:25PM +0400, Vasiliy Kulikov wrote: > ... > > > > No, I mean something else. Assume you have a task, which does the > > steps: > > > > 1) opens some sensitive file as root. This file is e.g. 0700. > > > > 2) mmaps the file via opened fd, either RO or RW. > > > > 3) closes fd. > > > > 4) drops root. > > > > Now it has a mapping of a privileged file, but cannot get fd of it > > anyhow. With map_files/ he may open his own /proc/$$/map_files/, pass > > ptrace() check, and get fd of the privileged file. He cannot explicitly > > open it as it is 0700, but he may open it via map_files/ and get RO/RW > > fd. > > > > Hi Vasiliy, could you please check if the update below address all your > concerns? Note that we still need at least RO access on such files. > > Cyrill > --- > fs, proc: Introduce the /proc/<pid>/map_files/ directory v14 > > From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> > > This one behaves similarly to the /proc/<pid>/fd/ one - it contains symlinks > one for each mapping with file, the name of a symlink is "vma->vm_start-vma->vm_end", > the target is the file. Opening a symlink results in a file that point exactly > to the same inode as them vma's one. > > For example the ls -l of some arbitrary /proc/<pid>/map_files/ > > | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so > | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1 > | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0 > | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so > | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so > > This *helps* checkpointing process in three ways: > > 1. When dumping a task mappings we do know exact file that is mapped by particular > region. We do this by opening /proc/$pid/map_files/address symlink the way we do > with file descriptors. s/address/$address/ for consistency. > > 2. This also helps in determining which anonymous shared mappings are shared with > each other by comparing the inodes of them. > > 3. When restoring a set of process s/process/processes/ > in case two of them has a mapping shared, we map > the memory by the 1st one and then open its /proc/$pid/map_files/address file and > map it by the 2nd task. How can you restore a set of processes in case they share an RW mapping as RW in both tasks if you deny opening /proc/$pid/map_files/$address as W? > Using /proc/$pid/maps for this is quite inconvenient since it brings repeatable > re-reading and reparsing for this text file which slows down restore procesure > significantly. Also as being pointed in (3) it is a way easier to use top level > shared mapping in children as /proc/$pid/map_files/address when needed. [...] > v14: (by Vasiliy Kulikov) > - for security reason the links are created with FMODE_READ mode > only even if the former file has FMODE_WRITE > - proc_map_files_lookup fails on any non-read-only queries. Do you have a PoC of the dumper? At least without the restorer. If we see an implementation of map_files/ user we probably identify what operation it needs and what security restrictions we have to define. Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
