mountinfo: get mount id from failed call to name_to_handle_at

Enables recursive remounting on very old kernels, which has some relevance
for SailfishOS community ports.

1 files changed, 37 insertions, 2 deletions

diff --git a/src/firejail/mountinfo.c b/src/firejail/mountinfo.c
index f1eb9c924..304f80eee 100644
--- a/src/firejail/mountinfo.c
+++ b/src/firejail/mountinfo.c
@@ -19,6 +19,7 @@
 */
 
 #include "firejail.h"
+#include <errno.h>
 
 #include <fcntl.h>
 #ifndef O_PATH
@@ -151,8 +152,35 @@ MountData *get_last_mount(void) {
         return &mdata;
 }
 
-// Needs kernel 3.15 or better
-int get_mount_id(int fd) {
+// Returns mount id, or -1 if fd refers to a procfs or sysfs file
+static int get_mount_id_from_handle(int fd) {
+        EUID_ASSERT();
+
+        char *proc;
+        if (asprintf(&proc, "/proc/self/fd/%d", fd) == -1)
+                errExit("asprintf");
+        struct file_handle *fh = malloc(sizeof *fh);
+        if (!fh)
+                errExit("malloc");
+        fh->handle_bytes = 0;
+
+        int rv = -1;
+        int tmp;
+        if (name_to_handle_at(-1, proc, fh, &tmp, AT_SYMLINK_FOLLOW) != -1) {
+                fprintf(stderr, "Error: unexpected result from name_to_handle_at\n");
+                exit(1);
+        }
+        if (errno == EOVERFLOW && fh->handle_bytes)
+                rv = tmp;
+
+        free(proc);
+        free(fh);
+        return rv;
+}
+
+// Returns mount id, or -1 on kernels < 3.15
+static int get_mount_id_from_fdinfo(int fd) {
+        EUID_ASSERT();
         int rv = -1;
 
         char *proc;
@@ -182,6 +210,13 @@ errexit:
         exit(1);
 }
 
+int get_mount_id(int fd) {
+        int rv = get_mount_id_from_fdinfo(fd);
+        if (rv < 0)
+                rv = get_mount_id_from_handle(fd);
+        return rv;
+}
+
 // Check /proc/self/mountinfo if path contains any mounts points.
 // Returns an array that can be iterated over for recursive remounting.
 char **build_mount_array(const int mount_id, const char *path) {