Hi Jann, On 04/05/2015 05:44 PM, Jann Horn wrote: > For the code that does this, see fs/dcache.c, search for > "prepend_unreachable". Thanks! Great patch! And thanks also for including the test code. I added one detail: this behavior was added in 2.6.36. Generally, it's useful to include the version where a behavior appeared. Also, I added the commit hash into the page source as a comment (that's often handy for future reference when editing the pages). See my commit 2b1f1a35b5 [1]. Cheers, Michael [1] http://git.kernel.org/cgit/docs/man-pages/man-pages.git/commit/?id=2b1f1a35b5f2d21fd6653b4cd4cb93f095e4b398 > repro testcase: > > $ cat getcwd.c > #define _GNU_SOURCE > #include <sched.h> > #include <unistd.h> > #include <stdio.h> > #include <limits.h> > #include <stdlib.h> > > int main(void) { > unshare(CLONE_NEWUSER | CLONE_NEWNS); > chdir("/usr"); > chroot("bin"); > > printf("current directory: \"%s\"\n", get_current_dir_name()); > > char *real = realpath(".", NULL); > printf("realpath of .: \"%s\"\n", real ? real : "{none}"); > real = realpath("../home/jann/.ssh", NULL); > printf("realpath of path: \"%s\"\n", real ? real : "{none}"); > > return 0; > } > $ cat getcwd_test.c > #define _GNU_SOURCE > #include <sched.h> > #include <unistd.h> > #include <stdio.h> > > int main(void) { > unshare(CLONE_NEWUSER | CLONE_NEWNS); > chdir("/usr"); > chroot("bin"); > printf("current directory: \"%s\"\n", get_current_dir_name()); > return 0; > } > $ gcc -o getcwd_test getcwd_test.c -Wall > $ ./getcwd_test > current directory: "(unreachable)/usr" > > realpath.3 doesn't currently seem to handle this > case in a sane way, so I'm not going to document > its behavior yet. I'll report that as a bug instead. > --- > man3/getcwd.3 | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/man3/getcwd.3 b/man3/getcwd.3 > index a1f7e2a..6a98b82 100644 > --- a/man3/getcwd.3 > +++ b/man3/getcwd.3 > @@ -80,6 +80,19 @@ The pathname is returned as the function result and via the argument > .IR buf , > if present. > > +If the current directory is not below the root directory of the current > +process (e.g. because the process set a new filesystem root > +using > +.BR chroot (2) > +without changing its current directory into the new root), the returned > +path will be prefixed with the string "(unreachable)". Such behavior can > +also be caused by an unprivileged user by changing the current directory > +into another mount namespace. > +When dealing with paths from untrusted sources, callers of these > +functions should consider checking whether the returned path starts > +with '/' or '(' to avoid misinterpreting an unreachable path > +as a relative path. > + > The > .BR getcwd () > function copies an absolute pathname of the current working directory > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
