> -----Original Message-----
> From: Xen-devel [mailto:[email protected]] On Behalf
> Of George Dunlap
> Sent: 05 November 2018 18:07
> To: [email protected]
> Cc: Anthony Perard <[email protected]>; Ian Jackson
> <[email protected]>; Wei Liu <[email protected]>; George Dunlap
> <[email protected]>
> Subject: [Xen-devel] [PATCH v4 5/6] tools/dm_depriv: Add first cut RLIMITs
>
> Limit the ability of a potentially compromised QEMU to consume system
> resources. Key limits:
> - RLIMIT_FSIZE (file size): 256KiB
> - RLIMIT_NPROC (after uid changes to a unique uid)
>
> Probably unnecessary limits but why not:
> - RLIMIT_CORE: 0
> - RLIMIT_MSGQUEUE: 0
> - RLIMIT_LOCKS: 0
> - RLIMIT_MEMLOCK: 0
>
> NB that we do not yet set RLIMIT_AS (total virtual memory) or
> RLIMIT_NOFILES (number of open files), since these require more care
> and/or more coordination with QEMU to implement.
>
> Suggested-by: Ross Lagerwall <[email protected]>
> Signed-off-by: George Dunlap <[email protected]>
> ---
> Changes since v3:
> - Align RLIMIT_ENTRY list for easier reading
> - Fix wrong format string specifier
> - Get rid of some trailing whitespace
>
> Changes since v2:
> - Use a macro to define rlimit entries
> - Use RLIMIT_NLIMITS as an end-of-list marker, rather than -1
> - Various style clean-ups
>
> CC: Ian Jackson <[email protected]>
> CC: Wei Liu <[email protected]>
> CC: Anthony Perard <[email protected]>
> ---
> docs/designs/qemu-deprivilege.md | 12 ++++-----
> tools/libxl/libxl_linux.c | 42 ++++++++++++++++++++++++++++++--
> 2 files changed, 46 insertions(+), 8 deletions(-)
>
> diff --git a/docs/designs/qemu-deprivilege.md b/docs/designs/qemu-
> deprivilege.md
> index a461ebbadd..e984064da6 100644
> --- a/docs/designs/qemu-deprivilege.md
> +++ b/docs/designs/qemu-deprivilege.md
> @@ -105,12 +105,6 @@ call:
>
> [qemu-namespaces]: https://lists.gnu.org/archive/html/qemu-devel/2017-
> 10/msg04723.html
>
> -# Restrictions / improvements still to do
> -
> -This lists potential restrictions still to do. It is meant to be
> -listed in order of ease of implementation, with low-hanging fruit
> -first.
> -
> ### Basic RLIMITs
>
> '''Description''': A number of limits on the resources that a given
> @@ -137,6 +131,12 @@ are specified; this does not apply to QEMU running as
> a Xen DM.
>
> '''Tested''': Not tested
>
> +# Restrictions / improvements still to do
> +
> +This lists potential restrictions still to do. It is meant to be
> +listed in order of ease of implementation, with low-hanging fruit
> +first.
> +
> ### Further RLIMITs
>
> RLIMIT_AS limits the total amount of memory; but this includes the
> diff --git a/tools/libxl/libxl_linux.c b/tools/libxl/libxl_linux.c
> index c7a345f4bb..ac9526d731 100644
> --- a/tools/libxl/libxl_linux.c
> +++ b/tools/libxl/libxl_linux.c
> @@ -12,11 +12,12 @@
> * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> * GNU Lesser General Public License for more details.
> */
> -
> +
Stray whitespace change?
> #include "libxl_osdeps.h" /* must come before any other headers */
>
> #include "libxl_internal.h"
> -
> +#include <sys/resource.h>
> +
Personally I tend to put local includes after ones from the include path. Is
there a reason it needs to come afterwards?
> int libxl__try_phy_backend(mode_t st_mode)
> {
> if (S_ISBLK(st_mode) || S_ISREG(st_mode)) {
> @@ -307,9 +308,31 @@ int libxl__pci_topology_init(libxl__gc *gc,
> return err;
> }
>
> +static struct {
> + int resource;
> + rlim_t limit;
> +} rlimits[] = {
> +#define RLIMIT_ENTRY(r, l) \
> + { .resource = r, .limit = l }
> + /* Big enough for log files, not big enough for a DoS */
> + RLIMIT_ENTRY(RLIMIT_FSIZE, 256*1024),
> +
> + /* Shouldn't need any of these */
> + RLIMIT_ENTRY(RLIMIT_NPROC, 0),
> + RLIMIT_ENTRY(RLIMIT_CORE, 0),
> + RLIMIT_ENTRY(RLIMIT_MSGQUEUE, 0),
> + RLIMIT_ENTRY(RLIMIT_LOCKS, 0),
> + RLIMIT_ENTRY(RLIMIT_MEMLOCK, 0),
> +
> + /* End-of-list marker */
> + RLIMIT_ENTRY(RLIMIT_NLIMITS, 0),
> +};
> +#undef RLIMIT_ENTRY
<pedantic> The undef should come before the brace to get the scoping correct.
</pedantic>
> +
> int libxl__local_dm_preexec_restrict(libxl__gc *gc)
> {
> int r;
> + unsigned i;
>
> /* Unshare mount and IPC namespaces. These are unused by QEMU. */
> r = unshare(CLONE_NEWNS | CLONE_NEWIPC);
> @@ -318,6 +341,21 @@ int libxl__local_dm_preexec_restrict(libxl__gc *gc)
> return ERROR_FAIL;
> }
>
> + /* Set various "easy" rlimits */
> + for (i = 0; rlimits[i].resource != RLIMIT_NLIMITS; i++) {
> + struct rlimit rlim;
> +
> + rlim.rlim_cur = rlim.rlim_max = rlimits[i].limit;
> +
> + r = setrlimit(rlimits[i].resource, &rlim);
> + if (r < 0) {
> + LOGE(ERROR, "Setting rlimit %d to %llu failed\n",
> + rlimits[i].resource,
> + (unsigned long long)rlimits[i].limit);
Indentation of the continuation lines looks odd (although libxl's coding style
is a mystery to me so they may be correct).
Paul
> + return ERROR_FAIL;
> + }
> + }
> +
> return 0;
> }
>
> --
> 2.19.1
>
>
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