Control: tags -1 + patch Hello!
I'm attaching a patch with a naive implementation of the suggestion made by Guillem Jover to compare mountinfo in case anyone finds it useful. Regards, Andreas Henriksson
--- ischroot.c.orig 2015-06-24 19:54:07.663058205 +0200 +++ ischroot.c 2015-06-24 20:10:49.660827291 +0200 @@ -2,6 +2,7 @@ * * Debian ischroot program * Copyright (C) 2011 Aurelien Jarno <[email protected]> + * Copyright (C) 2015 Andreas Henriksson <[email protected]> * * This is free software; see the GNU General Public License version 2 * or later for copying conditions. There is NO warranty. @@ -13,6 +14,7 @@ #include <string.h> #include <sys/stat.h> #include <sys/types.h> +#include <fcntl.h> #include <unistd.h> #ifdef HAVE_GETOPT_H #include <getopt.h> @@ -51,6 +53,73 @@ #if defined (__linux__) +/* ischroot_mountinfo returns: + * negative value on failure, + * 0 on chroot detected, + * 1 on no chroot detected. + */ +static int ischroot_mountinfo() +{ + char buf1[1024], buf2[1024]; + int fd1, fd2; + ssize_t rlen1, rlen2; + int ret; + + fd1 = open("/proc/1/mountinfo", O_RDONLY); + fd2 = open("/proc/self/mountinfo", O_RDONLY); + + if (fd1 < 0 || fd2 < 0) { + ret = -1; + goto out; + } + + do { + rlen1 = read(fd1, buf1, sizeof(buf1)); + rlen2 = read(fd2, buf2, sizeof(buf2)); + + if (rlen1 < 0 || rlen2 < 0) { + /* TODO: could do a better job of handling errors like EAGAIN here if + * relevant. Investigate possible error codes returned for procfs by + * kernel. + */ + ret = -1; + goto out; + } + + /* FIXME: we assume read always fills up the buffer if there are more + * contents to read, which is not correct. Theoretically read can return + * smaller chunks, so we should probably memcmp the minimum of the return + * values and shift both buffer contents and try to fill it up by + * appending and continue comparing. + * Check if this is a problem in practise... + */ + + if (rlen1 != rlen2) { + ret = 0; + goto out; + } + + if (memcmp(buf1, buf2, rlen1) != 0) { + ret = 0; + goto out; + } + + } while (rlen1 > 0 && rlen2 > 0); + + if (rlen1 == 0 && rlen2 == 0) + ret = 1; + else + ret = -1; + +out: + if (fd1 >= 0) + close(fd1); + if (fd2 >= 0) + close(fd2); + + return ret; +} + /* On Linux we can detect chroots by checking if the * devicenumber/inode pair of / are the same as that of * /sbin/init's. This may fail if not running as root or if @@ -64,6 +133,11 @@ static int ischroot() { struct stat st1, st2; + int ret; + + ret = ischroot_mountinfo(); + if (ret >= 0) + return ret; if (stat("/", &st1)) return 2;
