On 11/06/2018 09:22 AM, Paul Durrant wrote:
>> -----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?
Got rid of trailing witespace; I mentioned it under "Changes since v3".
>> #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?
No reason; just habit to add things to the end. I'll move it earlier
unless Ian objects.
>> +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>
Sure.
>> +
>> 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).
Don't think it says anything about this case; I find having the
arguments indented beyond the format string easier to read.
-George
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