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restore: Do fchroot() via proc helpers

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There's no such thing as fchroot() in Linux, but we need to do
chroot() into existing file descriptor. Before this patch we did
this by chroot()-ing into /proc/self/fd/$fd. W/o proc mounted it's
no longer possible, so do this like

fchdir(proc_service_fd);
chroot("./self/fd/$root_fd");
fchdir($cwd_fd);

Thanks to Andrey Vagin for this trick ;)

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
This commit is contained in:
Pavel Emelyanov 2014-06-05 20:18:41 +04:00
parent 3659d60ab7
commit 701f883765
1 changed files with 28 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

46
files.c
View file

@ -997,13 +997,23 @@ out:
static int fchroot(int fd)
{
char fd_path[PSFDS];
int proc;
/*
* There's no such thing in syscalls. We can emulate
* it using the /proc/self/fd/ :)
*
* But since there might be no /proc mount in our mount
* namespace, we will have to ... workaround it.
*/
sprintf(fd_path, "/proc/self/fd/%d", fd);
proc = get_service_fd(PROC_FD_OFF);
if (fchdir(proc) < 0) {
pr_perror("Can't chdir to proc");
return -1;
}
sprintf(fd_path, "./self/fd/%d", fd);
pr_debug("Going to chroot into %s\n", fd_path);
return chroot(fd_path);
}
@ -1020,23 +1030,6 @@ int prepare_fs(int pid)
if (pb_read_one(ifd, &fe, PB_FS) < 0)
goto out_i;
/*
* Restore CWD
*/
dd = open_reg_by_id(fe->cwd_id);
if (dd < 0) {
pr_err("Can't open cwd %#x\n", fe->cwd_id);
goto err;
}
ret = fchdir(dd);
close(dd);
if (ret < 0) {
pr_perror("Can't change cwd");
goto err;
}
/*
* Restore root
*/
@ -1054,6 +1047,23 @@ int prepare_fs(int pid)
goto err;
}
/*
* Restore CWD
*/
dd = open_reg_by_id(fe->cwd_id);
if (dd < 0) {
pr_err("Can't open cwd %#x\n", fe->cwd_id);
goto err;
}
ret = fchdir(dd);
close(dd);
if (ret < 0) {
pr_perror("Can't change cwd");
goto err;
}
if (fe->has_umask) {
pr_info("Restoring umask to %o\n", fe->umask);
umask(fe->umask);