On 14.01.2016 01:09, Serge Hallyn wrote: > Quoting Bogdan Purcareata (bogdan.purcare...@nxp.com): >> On 11.01.2016 20:59, Serge Hallyn wrote: >>> Quoting Bogdan Purcareata (bogdan.purcare...@nxp.com): >>>> The safe_mount primitive will mount the fs in the new container >>>> environment by using file descriptors referred in /proc/self/fd. >>>> However, when the mounted filesystem is proc itself, it will have >>>> been previously unmounted, therefore resulting in an error when >>>> searching for these file descriptors. This only happens when there's >>>> no container rootfs prefix (commonly with lxc-execute). >>>> >>>> Implement the support for this use case as well, by doing the mount >>>> based on the full path. >>>> >>>> Refactor the whole function in order to remove duplicated code checks >>>> and improve readability. >>>> >>>> Changes since v1: >>>> - In order to address CVE-2015-1335, still check if the destination is >>>> not a symlink. Do the mount only if the destination file descriptor >>>> exists. >>>> >>>> Signed-off-by: Bogdan Purcareata <bogdan.purcare...@nxp.com> >>>> --- >>>> src/lxc/utils.c | 49 ++++++++++++++++++++++++++++--------------------- >>>> 1 file changed, 28 insertions(+), 21 deletions(-) >>>> >>>> diff --git a/src/lxc/utils.c b/src/lxc/utils.c >>>> index d9e769d..c53711a 100644 >>>> --- a/src/lxc/utils.c >>>> +++ b/src/lxc/utils.c >>>> @@ -1644,9 +1644,9 @@ out: >>>> int safe_mount(const char *src, const char *dest, const char *fstype, >>>> unsigned long flags, const void *data, const char >>>> *rootfs) >>>> { >>>> - int srcfd = -1, destfd, ret, saved_errno; >>>> + int srcfd = -1, destfd = -1, ret = 0; >>>> char srcbuf[50], destbuf[50]; // only needs enough for >>>> /proc/self/fd/<fd> >>>> - const char *mntsrc = src; >>>> + const char *mntsrc = src, *mntdest = dest; >>>> >>>> if (!rootfs) >>>> rootfs = ""; >>>> @@ -1655,45 +1655,52 @@ int safe_mount(const char *src, const char *dest, >>>> const char *fstype, >>>> if (flags & MS_BIND && src && src[0] != '/') { >>>> INFO("this is a relative bind mount"); >>>> srcfd = open_without_symlink(src, NULL); >>>> - if (srcfd < 0) >>>> - return srcfd; >>>> + if (srcfd < 0) { >>>> + ret = srcfd; >>>> + goto out; >>>> + } >>>> ret = snprintf(srcbuf, 50, "/proc/self/fd/%d", srcfd); >>>> if (ret < 0 || ret > 50) { >>>> - close(srcfd); >>>> ERROR("Out of memory"); >>>> - return -EINVAL; >>>> + ret = -EINVAL; >>>> + goto out_src; >>>> } >>>> mntsrc = srcbuf; >>>> } >>>> >>>> destfd = open_without_symlink(dest, rootfs); >>>> if (destfd < 0) { >>>> - if (srcfd != -1) >>>> - close(srcfd); >>>> - return destfd; >>>> + ret = destfd; >>>> + goto out_src; >>>> } >>>> >>>> ret = snprintf(destbuf, 50, "/proc/self/fd/%d", destfd); >>>> if (ret < 0 || ret > 50) { >>>> - if (srcfd != -1) >>>> - close(srcfd); >>>> - close(destfd); >>>> ERROR("Out of memory"); >>>> - return -EINVAL; >>>> + ret = -EINVAL; >>>> + goto out_dest; >>>> } >>>> >>>> - ret = mount(mntsrc, destbuf, fstype, flags, data); >>>> - saved_errno = errno; >>>> - if (srcfd != -1) >>>> - close(srcfd); >>>> - close(destfd); >>>> + /* make sure the destination descriptor exists */ >>>> + if (access(destbuf, F_OK) == 0) >>>> + mntdest = destbuf; >>> First, if we're going to shortcut I'd prefer to say "if /proc/self >>> does not exist then skip this check" fo rnow. >>> But can we think of any way to still do this check? >>> >>> What exactly are the cases? >>> >>> 1. lxc-execute, lxc-init tries to mount /proc. We should be able >>> to simply have lxc always mount /proc before the pivot_root, so >>> we can properly do this check. >>> >>> what use-cases will break if we demand /proc to exist in the >>> container? (We can add an option to umount /proc in lxc-init, >>> but the directory would have to exist) >> That's my use case - the failing function is tmp_proc_mount, thus happening > > Wait, is your rootfs NULL or not?
Yep, it's NULL - plain "lxc-execute -n foo -f empty.conf -- bash". > We can handle that case specially. > > mount_proc_if_needed() is only called from tmp_proc_mount(), which is only > called from lxc_setup(). If rootfs is NULL, then all bets are off anyway > and we can just call mount(). If rootfs is not NULL, then we're mounting > in a separate container rootfs and we should use safe_mount(), but we > expect the real /proc to then exist. In that case, would the following fix be more appropriate? @@ -1747,8 +1747,14 @@ int mount_proc_if_needed(const char *rootfs) return 0; domount: - if (safe_mount("proc", path, "proc", 0, NULL, rootfs) < 0) + if (!strcmp(rootfs,"")) /* rootfs is NULL */ + ret = mount("proc", path, "proc", 0, NULL); + else + ret = safe_mount("proc", path, "proc", 0, NULL, rootfs); + + if (ret < 0) return -1; + INFO("Mounted /proc in container for security transition"); return 1; } Btw checking for the rootfs to be NULL is done this way since mount_proc_if_needed is called like: mount_proc_if_needed(lxc_conf->rootfs.path ? lxc_conf->rootfs.mount : ""); Thanks! Bogdan P. _______________________________________________ lxc-devel mailing list lxc-devel@lists.linuxcontainers.org http://lists.linuxcontainers.org/listinfo/lxc-devel