[PATCH v2 04/19] elf: Add all malloc tunable to unsecvars
Siddhesh Poyarekar
siddhesh@sourceware.org
Wed Oct 18 13:04:48 GMT 2023
On 2023-10-17 09:05, Adhemerval Zanella wrote:
> Some environment variables allow alteration of allocator behavior
> across setuid boundaries, where a setuid program may ignore the
> tunable, but its non-setuid child can read it and adjust the memory
> allocator behavior accordingly.
>
> Most library behavior tunings is limited to the current process and does
> not bleed in scope; so it is unclear how pratical this misfeature is.
> If behavior change across privilege boundaries is desirable, it would be
> better done with a wrapper program around the non-setuid child that sets
> these envvars, instead of using the setuid process as the messenger.
>
> The patch as fixes tst-env-setuid, where it fail if any unsecvars is
> set. It also adds a dynamic test, although it requires
> --enable-hardcoded-path-in-tests so kernel correctly sets the setuid
> bit (using the loader command directly would require to set the
> setuid bit on the loader itself, which is not a usual deployment).
>
> Co-authored-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
Likewise, I'll leave this for someone else since I am a co-author.
Thanks,
Sid
>
> Checked on x86_64-linux-gnu.
> ---
> elf/Makefile | 8 +--
> elf/tst-env-setuid-static.c | 1 +
> elf/tst-env-setuid.c | 128 +++++++++++++++++++++---------------
> sysdeps/generic/unsecvars.h | 7 ++
> 4 files changed, 86 insertions(+), 58 deletions(-)
> create mode 100644 elf/tst-env-setuid-static.c
>
> diff --git a/elf/Makefile b/elf/Makefile
> index c824f7dab7..f1cd6e13fa 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -262,7 +262,7 @@ tests-static-normal := \
> tst-array5-static \
> tst-dl-iter-static \
> tst-dst-static \
> - tst-env-setuid \
> + tst-env-setuid-static \
> tst-getauxval-static \
> tst-linkall-static \
> tst-single_threaded-pthread-static \
> @@ -305,6 +305,7 @@ tests := \
> tst-array5 \
> tst-auxv \
> tst-dl-hash \
> + tst-env-setuid \
> tst-leaks1 \
> tst-stringtable \
> tst-tls9 \
> @@ -2467,9 +2468,6 @@ $(objpfx)tst-nodelete-dlclose: $(objpfx)tst-nodelete-dlclose-dso.so
> $(objpfx)tst-nodelete-dlclose.out: $(objpfx)tst-nodelete-dlclose-dso.so \
> $(objpfx)tst-nodelete-dlclose-plugin.so
>
> -tst-env-setuid-ENV = MALLOC_CHECK_=2 MALLOC_MMAP_THRESHOLD_=4096 \
> - LD_HWCAP_MASK=0x1
> -
> $(objpfx)tst-debug1.out: $(objpfx)tst-debug1mod1.so
>
> $(objpfx)tst-debug1mod1.so: $(objpfx)testobj1.so
> @@ -3021,3 +3019,5 @@ LDFLAGS-tst-dlclose-lazy-mod1.so = -Wl,-z,lazy,--no-as-needed
> $(objpfx)tst-dlclose-lazy-mod1.so: $(objpfx)tst-dlclose-lazy-mod2.so
> $(objpfx)tst-dlclose-lazy.out: \
> $(objpfx)tst-dlclose-lazy-mod1.so $(objpfx)tst-dlclose-lazy-mod2.so
> +
> +tst-env-setuid-ARGS = -- $(host-test-program-cmd)
> diff --git a/elf/tst-env-setuid-static.c b/elf/tst-env-setuid-static.c
> new file mode 100644
> index 0000000000..0d88ae88b9
> --- /dev/null
> +++ b/elf/tst-env-setuid-static.c
> @@ -0,0 +1 @@
> +#include "tst-env-setuid.c"
> diff --git a/elf/tst-env-setuid.c b/elf/tst-env-setuid.c
> index 032ab44be2..ba295a6a14 100644
> --- a/elf/tst-env-setuid.c
> +++ b/elf/tst-env-setuid.c
> @@ -15,18 +15,14 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> -/* Verify that tunables correctly filter out unsafe environment variables like
> - MALLOC_CHECK_ and MALLOC_MMAP_THRESHOLD_ but also retain
> - MALLOC_MMAP_THRESHOLD_ in an unprivileged child. */
> +/* Verify that correctly filter out unsafe environment variables defined
> + in unsecvars.h. */
>
> -#include <errno.h>
> -#include <fcntl.h>
> -#include <stdlib.h>
> -#include <stdint.h>
> +#include <array_length.h>
> +#include <gnu/lib-names.h>
> #include <stdio.h>
> +#include <stdlib.h>
> #include <string.h>
> -#include <sys/stat.h>
> -#include <sys/wait.h>
> #include <unistd.h>
>
> #include <support/check.h>
> @@ -36,61 +32,72 @@
>
> static char SETGID_CHILD[] = "setgid-child";
>
> -#ifndef test_child
> -static int
> -test_child (void)
> -{
> - if (getenv ("MALLOC_CHECK_") != NULL)
> - {
> - printf ("MALLOC_CHECK_ is still set\n");
> - return 1;
> - }
> -
> - if (getenv ("MALLOC_MMAP_THRESHOLD_") == NULL)
> - {
> - printf ("MALLOC_MMAP_THRESHOLD_ lost\n");
> - return 1;
> - }
> +#define FILTERED_VALUE "some-filtered-value"
> +#define UNFILTERED_VALUE "some-unfiltered-value"
>
> - if (getenv ("LD_HWCAP_MASK") != NULL)
> - {
> - printf ("LD_HWCAP_MASK still set\n");
> - return 1;
> - }
> +struct envvar_t
> +{
> + const char *env;
> + const char *value;
> +};
>
> - return 0;
> -}
> -#endif
> +/* That is not an extensible list of all filtered out environment
> + variables. */
> +static const struct envvar_t filtered_envvars[] =
> +{
> + { "GLIBC_TUNABLES", FILTERED_VALUE },
> + { "LD_AUDIT", FILTERED_VALUE },
> + { "LD_HWCAP_MASK", FILTERED_VALUE },
> + { "LD_LIBRARY_PATH", FILTERED_VALUE },
> + { "LD_PRELOAD", FILTERED_VALUE },
> + { "LD_PROFILE", FILTERED_VALUE },
> + { "MALLOC_ARENA_MAX", FILTERED_VALUE },
> + { "MALLOC_PERTURB_", FILTERED_VALUE },
> + { "MALLOC_TRACE", FILTERED_VALUE },
> + { "MALLOC_TRIM_THRESHOLD_", FILTERED_VALUE },
> + { "RES_OPTIONS", FILTERED_VALUE },
> +};
> +
> +static const struct envvar_t unfiltered_envvars[] =
> +{
> + { "LD_BIND_NOW", "0" },
> + { "LD_BIND_NOT", "1" },
> + /* Non longer supported option. */
> + { "LD_ASSUME_KERNEL", UNFILTERED_VALUE },
> +};
>
> -#ifndef test_parent
> static int
> -test_parent (void)
> +test_child (void)
> {
> - if (getenv ("MALLOC_CHECK_") == NULL)
> - {
> - printf ("MALLOC_CHECK_ lost\n");
> - return 1;
> - }
> + int ret = 0;
>
> - if (getenv ("MALLOC_MMAP_THRESHOLD_") == NULL)
> + for (const struct envvar_t *e = filtered_envvars;
> + e != array_end (filtered_envvars);
> + e++)
> {
> - printf ("MALLOC_MMAP_THRESHOLD_ lost\n");
> - return 1;
> + const char *env = getenv (e->env);
> + ret |= env != NULL;
> }
>
> - if (getenv ("LD_HWCAP_MASK") == NULL)
> + for (const struct envvar_t *e = unfiltered_envvars;
> + e != array_end (unfiltered_envvars);
> + e++)
> {
> - printf ("LD_HWCAP_MASK lost\n");
> - return 1;
> + const char *env = getenv (e->env);
> + ret |= !(env != NULL && strcmp (env, e->value) == 0);
> }
>
> - return 0;
> + return ret;
> }
> -#endif
>
> static int
> do_test (int argc, char **argv)
> {
> + /* For dynamic loader, the test requires --enable-hardcoded-path-in-tests so
> + the kernel sets the AT_SECURE on process initialization. */
> + if (argc >= 2 && strstr (argv[1], LD_SO) != 0)
> + FAIL_UNSUPPORTED ("dynamic test requires --enable-hardcoded-path-in-tests");
> +
> /* Setgid child process. */
> if (argc == 2 && strcmp (argv[1], SETGID_CHILD) == 0)
> {
> @@ -104,20 +111,33 @@ do_test (int argc, char **argv)
> if (ret != 0)
> exit (1);
>
> - exit (EXIT_SUCCESS);
> + /* Special return code to make sure that the child executed all the way
> + through. */
> + exit (42);
> }
> else
> {
> - if (test_parent () != 0)
> - exit (1);
> + for (const struct envvar_t *e = filtered_envvars;
> + e != array_end (filtered_envvars);
> + e++)
> + setenv (e->env, e->value, 1);
> +
> + for (const struct envvar_t *e = unfiltered_envvars;
> + e != array_end (unfiltered_envvars);
> + e++)
> + setenv (e->env, e->value, 1);
>
> int status = support_capture_subprogram_self_sgid (SETGID_CHILD);
>
> if (WEXITSTATUS (status) == EXIT_UNSUPPORTED)
> - return EXIT_UNSUPPORTED;
> -
> - if (!WIFEXITED (status))
> - FAIL_EXIT1 ("Unexpected exit status %d from child process\n", status);
> + exit (EXIT_UNSUPPORTED);
> +
> + if (WEXITSTATUS (status) != 42)
> + {
> + printf (" child failed with status %d\n",
> + WEXITSTATUS (status));
> + support_record_failure ();
> + }
>
> return 0;
> }
> diff --git a/sysdeps/generic/unsecvars.h b/sysdeps/generic/unsecvars.h
> index 81397fb90b..f7ebed60e5 100644
> --- a/sysdeps/generic/unsecvars.h
> +++ b/sysdeps/generic/unsecvars.h
> @@ -18,7 +18,14 @@
> "LD_SHOW_AUXV\0" \
> "LOCALDOMAIN\0" \
> "LOCPATH\0" \
> + "MALLOC_ARENA_MAX\0" \
> + "MALLOC_ARENA_TEST\0" \
> + "MALLOC_MMAP_MAX_\0" \
> + "MALLOC_MMAP_THRESHOLD_\0" \
> + "MALLOC_PERTURB_\0" \
> + "MALLOC_TOP_PAD_\0" \
> "MALLOC_TRACE\0" \
> + "MALLOC_TRIM_THRESHOLD_\0" \
> "NIS_PATH\0" \
> "NLSPATH\0" \
> "RESOLV_HOST_CONF\0" \
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