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seccomp: allow shmat to be a separate syscall on architectures which use a multiplexer 

After
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0d6040d46817,
those syscalls have their separate numbers and we can block them.
But glibc might still use the old ones. So let's just do a best-effort
block and not assume anything about how effective it is.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2019-03-15 12:46:56 +01:00
parent e55bdf9b6c
commit 67fb5f338f
2 changed files with 8 additions and 4 deletions
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3
src/shared/seccomp-util.c
View File

@ -1519,6 +1519,7 @@ int seccomp_memory_deny_write_execute(void) {
case SCMP_ARCH_X86:
filter_syscall = SCMP_SYS(mmap2);
block_syscall = SCMP_SYS(mmap);
shmat_syscall = SCMP_SYS(shmat);
break;
case SCMP_ARCH_PPC:
@ -1585,7 +1586,7 @@ int seccomp_memory_deny_write_execute(void) {
continue;
#endif
if (shmat_syscall != 0) {
if (shmat_syscall > 0) {
r = add_seccomp_syscall_filter(seccomp, arch, SCMP_SYS(shmat),
1,
SCMP_A2(SCMP_CMP_MASKED_EQ, SHM_EXEC, SHM_EXEC));

9
src/test/test-seccomp.c
View File

@ -548,15 +548,18 @@ static void test_memory_deny_write_execute_shmat(void) {
assert_se(seccomp_memory_deny_write_execute() >= 0);
p = shmat(shmid, NULL, SHM_EXEC);
log_debug_errno(p == MAP_FAILED ? errno : 0, "shmat(SHM_EXEC): %m");
#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__)
assert_se(p == MAP_FAILED);
assert_se(errno == EPERM);
#else /* __i386__, __powerpc64__, and "unknown" architectures */
assert_se(p != MAP_FAILED);
assert_se(shmdt(p) == 0);
#endif
/* Depending on kernel, libseccomp, and glibc versions, other architectures
* might fail or not. Let's not assert success. */
if (p != MAP_FAILED)
assert_se(shmdt(p) == 0);
p = shmat(shmid, NULL, 0);
log_debug_errno(p == MAP_FAILED ? errno : 0, "shmat(0): %m");
assert_se(p != MAP_FAILED);
assert_se(shmdt(p) == 0);