On Mon, Jan 26, 2015 at 3:43 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 27 Jan 2015 00:00:54 +0300 Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote: > >> On Mon, Jan 26, 2015 at 02:47:31PM +0200, Kirill A. Shutemov wrote: >> > On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote: >> > > Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and >> > > is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface >> > > is very useful for enumerating the files mapped into a process when >> > > the more verbose information in /proc/<pid>/maps is not needed. > > This is the main (actually only) justification for the patch, and it it > far too thin. What does "not needed" mean. Why can't people just use > /proc/pid/maps? > >> > > This patch moves the folder out from behind CHECKPOINT_RESTORE, and >> > > removes the CAP_SYS_ADMIN restrictions. Following the links requires >> > > the ability to ptrace the process in question, so this doesn't allow >> > > an attacker to do anything they couldn't already do before. >> > > >> > > Signed-off-by: Calvin Owens <calvinowens@xxxxxx> >> > >> > Cc +linux-api@ >> >> Looks good to me, thanks! Though I would really appreciate if someone >> from security camp take a look as well. > > hm, who's that. Kees comes to mind. > > And reviewers' task would be a heck of a lot easier if they knew what > /proc/pid/map_files actually does. This: > > akpm3:/usr/src/25> grep -r map_files Documentation If akpm's comments weren't clear: this needs to be fixed. Everything in /proc should appear in Documentation. > akpm3:/usr/src/25> > > does not help. > > The 640708a2cff7f81 changelog says: > > : 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 How is mmap offset represented in this output? > > afacit this info is also available in /proc/pid/maps, so things > shouldn't get worse if the /proc/pid/map_files permissions are at least > as restrictive as the /proc/pid/maps permissions. Is that the case? > (Please add to changelog). Both maps and map_files uses ptrace_may_access (via mm_acces) with PTRACE_MODE_READ, so I'm happy from a info leak perspective. Are mount namespaces handled in this output? > There's one other problem here: we're assuming that the map_files > implementation doesn't have bugs. If it does have bugs then relaxing > permissions like this will create new vulnerabilities. And the > map_files implementation is surprisingly complex. Is it bug-free? -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
