Use ProcMountNSGuard in C API

This commit adds helper method in C API using `ProcMountNSGuard` to enter
and exit mount namespace, and use it in `libbpf.h`

src/cc/CMakeLists.txt

@@ -39,8 +39,8 @@ add_library(bcc-shared SHARED bpf_common.cc bpf_module.cc libbpf.c perf_reader.c
 set_target_properties(bcc-shared PROPERTIES VERSION ${REVISION_LAST} SOVERSION 0)
 set_target_properties(bcc-shared PROPERTIES OUTPUT_NAME bcc)
 
-add_library(bcc-loader-static STATIC libbpf.c perf_reader.c bcc_elf.c bcc_perf_map.c bcc_proc.c)
-add_library(bcc-static STATIC bpf_common.cc bpf_module.cc shared_table.cc bpffs_table.cc json_map_decl_visitor.cc table_storage.cc exported_files.cc bcc_syms.cc usdt_args.cc usdt.cc common.cc BPF.cc BPFTable.cc)
+add_library(bcc-loader-static STATIC libbpf.c perf_reader.c bcc_elf.c bcc_perf_map.c bcc_proc.c bcc_syms.cc)
+add_library(bcc-static STATIC bpf_common.cc bpf_module.cc shared_table.cc bpffs_table.cc json_map_decl_visitor.cc table_storage.cc exported_files.cc usdt_args.cc usdt.cc common.cc BPF.cc BPFTable.cc)
 set_target_properties(bcc-static PROPERTIES OUTPUT_NAME bcc)
 
 set(llvm_raw_libs bitwriter bpfcodegen irreader linker

src/cc/bcc_proc.c

@@ -13,15 +13,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE
-#endif
 
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/mman.h>
 #include <fcntl.h>
-#include <sched.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <stdbool.h>
@@ -393,97 +389,6 @@ void bcc_procutils_free(const char *ptr) {
   free((void *)ptr);
 }
 
-bool bcc_procutils_enter_mountns(int pid, struct ns_cookie *nc) {
-  char curnspath[4096];
-  char newnspath[4096];
-  int oldns = -1;
-  int newns = -1;
-  struct stat ons_stat;
-  struct stat nns_stat;
-
-  if (nc == NULL)
-    return false;
-
-  nc->nsc_oldns = -1;
-  nc->nsc_newns = -1;
-
-  if (snprintf(curnspath, 4096, "/proc/self/ns/mnt") == 4096) {
-    return false;
-  }
-
-  if (snprintf(newnspath, 4096, "/proc/%d/ns/mnt", pid) == 4096) {
-    return false;
-  }
-
-  if ((oldns = open(curnspath, O_RDONLY)) < 0) {
-    return false;
-  }
-
-  if ((newns = open(newnspath, O_RDONLY)) < 0) {
-    goto errout;
-  }
-
-  if (fstat(oldns, &ons_stat) < 0) {
-    goto errout;
-  }
-
-  if (fstat(newns, &nns_stat) < 0) {
-    goto errout;
-  }
-
-  /*
-   * Only switch to the new namespace if it doesn't match the existing
-   * namespace.  This prevents us from getting an EPERM when trying to enter an
-   * identical namespace.
-   */
-  if (ons_stat.st_ino == nns_stat.st_ino) {
-    goto errout;
-  }
-
-  if (setns(newns, CLONE_NEWNS) < 0) {
-    goto errout;
-  }
-
-  nc->nsc_oldns = oldns;
-  nc->nsc_newns = newns;
-
-  return true;
-
-errout:
-  if (oldns > -1) {
-    (void) close(oldns);
-  }
-  if (newns > -1) {
-    (void) close(newns);
-  }
-  return false;
-}
-
-bool bcc_procutils_exit_mountns(struct ns_cookie *nc) {
-  bool rc = false;
-
-  if (nc == NULL)
-    return rc;
-
-  if (nc->nsc_oldns == -1 || nc->nsc_newns == -1)
-    return rc;
-
-  if (setns(nc->nsc_oldns, CLONE_NEWNS) == 0) {
-    rc = true;
-  }
-
-  if (nc->nsc_oldns > -1) {
-    (void) close(nc->nsc_oldns);
-    nc->nsc_oldns = -1;
-  }
-  if (nc->nsc_newns > -1) {
-    (void) close(nc->nsc_newns);
-    nc->nsc_newns = -1;
-  }
-
-  return rc;
-}
-
 /* Detects the following languages + C. */
 const char *languages[] = {"java", "python", "ruby", "php", "node"};
 const char *language_c = "c";

src/cc/bcc_proc.h

@@ -24,11 +24,6 @@ extern "C" {
 
 #include <stdint.h>
 
-struct ns_cookie {
-  int nsc_oldns;
-  int nsc_newns;
-};
-
 // Module name, start address, end address, whether to check mount namespace, payload
 typedef int (*bcc_procutils_modulecb)(const char *, uint64_t, uint64_t, bool, void *);
 // Symbol name, address, payload
@@ -41,8 +36,6 @@ int bcc_procutils_each_module(int pid, bcc_procutils_modulecb callback,
                               void *payload);
 int bcc_procutils_each_ksym(bcc_procutils_ksymcb callback, void *payload);
 void bcc_procutils_free(const char *ptr);
-bool bcc_procutils_enter_mountns(int pid, struct ns_cookie *nc);
-bool bcc_procutils_exit_mountns(struct ns_cookie *nc);
 const char *bcc_procutils_language(int pid);
 
 #ifdef __cplusplus

src/cc/bcc_syms.cc

@@ -517,4 +517,15 @@ int bcc_resolve_symname(const char *module, const char *symname,
   sym->offset = (sym->offset - load_addr);
   return 0;
 }
+
+void *bcc_enter_mount_ns(int pid) {
+  return static_cast<void *>(new ProcMountNSGuard(pid));
+}
+
+void bcc_exit_mount_ns(void **guard) {
+  if (guard && *guard) {
+    delete static_cast<ProcMountNSGuard *>(*guard);
+    *guard = NULL;
+  }
+}
 }

src/cc/bcc_syms.h

@@ -52,6 +52,10 @@ int bcc_foreach_symbol(const char *module, SYM_CB cb);
 int bcc_find_symbol_addr(struct bcc_symbol *sym);
 int bcc_resolve_symname(const char *module, const char *symname,
                         const uint64_t addr, int pid, struct bcc_symbol *sym);
+
+void *bcc_enter_mount_ns(int pid);
+void bcc_exit_mount_ns(void **guard);
+
 #ifdef __cplusplus
 }
 #endif

src/cc/libbpf.c

@@ -38,7 +38,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 
-#include "bcc_proc.h"
+#include "bcc_syms.h"
 #include "libbpf.h"
 #include "perf_reader.h"
 
@@ -413,8 +413,8 @@ void * bpf_attach_uprobe(int progfd, enum bpf_probe_attach_type attach_type, con
   char new_name[128];
   struct perf_reader *reader = NULL;
   static char *event_type = "uprobe";
-  struct ns_cookie nsc = {-1, -1};
   int n;
+  void* mount_ns_guard = NULL;
 
   snprintf(new_name, sizeof(new_name), "%s_bcc_%d", ev_name, getpid());
   reader = perf_reader_new(cb, NULL, NULL, cb_cookie, probe_perf_reader_page_cnt);
@@ -435,15 +435,15 @@ void * bpf_attach_uprobe(int progfd, enum bpf_probe_attach_type attach_type, con
     goto error;
   }
 
-  bcc_procutils_enter_mountns(pid, &nsc);
+  mount_ns_guard = bcc_enter_mount_ns(pid);
   if (write(kfd, buf, strlen(buf)) < 0) {
     if (errno == EINVAL)
       fprintf(stderr, "check dmesg output for possible cause\n");
     close(kfd);
     goto error;
   }
-  bcc_procutils_exit_mountns(&nsc);
   close(kfd);
+  bcc_exit_mount_ns(&mount_ns_guard);
 
   snprintf(buf, sizeof(buf), "/sys/kernel/debug/tracing/events/%ss/%s", event_type, new_name);
   if (bpf_attach_tracing_event(progfd, buf, reader, pid, cpu, group_fd) < 0)
@@ -452,7 +452,7 @@ void * bpf_attach_uprobe(int progfd, enum bpf_probe_attach_type attach_type, con
   return reader;
 
 error:
-  bcc_procutils_exit_mountns(&nsc);
+  bcc_exit_mount_ns(&mount_ns_guard);
   perf_reader_free(reader);
   return NULL;
 }