lnstools

commit a0935155f8491fc179f94e8b9e2f571f3dae8c6d
parent aa5b18e25764291a1b23976fad0bb49182daba75
Author: Jan Pobrislo <ccx@te2000.cz>
Date:   Fri, 12 Dec 2025 01:38:10 +0000

normalize pivot_root paths, use put_old suffix only for umount

Diffstat:
M
src/lns-lockdown_main.c
 | 
39
+++++++++++++++++++++++++++++++--------

1 file changed, 31 insertions(+), 8 deletions(-)
diff --git a/src/lns-lockdown_main.c b/src/lns-lockdown_main.c
@@ -61,15 +61,28 @@ int stralloc_catenv0(stralloc *sa, char const * env_name) {
 
 /*** individual steps of dropping into sandbox ***/
 void pivot_and_umount(
-    char const *const old_place_for_new_root,
-    char const *const new_place_for_old_root,
+    char const *const new_root,
+    char const *const put_old,
     struct unexport_s *const unex
 ) {
+    size_t newroot_len = 0;
+    for(size_t char_n=0; new_root[char_n]; char_n++) {
+        if(new_root[char_n] == 0) {
+            newroot_len = char_n;
+            break;
+        }
+        if(new_root[char_n] != put_old[char_n]) {
+            strerr_dief1x(100, "first path is not prefix of second path");
+        }
+        if(char_n > PATH_MAX) {
+            strerr_dief1x(111, "realpath() returned invalid string");
+        }
+    }
     size_t mtp_count, mtp_n;
-    int oldroot_len = strlen(new_place_for_old_root);
+    size_t oldroot_len = strlen(put_old) - newroot_len;
     stralloc sa_env = STRALLOC_ZERO;
     stralloc sa_mtp = STRALLOC_ZERO;
-    if (!stralloc_catb(&sa_mtp, new_place_for_old_root, oldroot_len)) {
+    if (!stralloc_catb(&sa_mtp, &put_old[newroot_len], oldroot_len)) {
         strerr_diefu1sys(111, "store mount path");
     }
     if (!size_scan(getenv_dienotset("NS_MTP_COUNT"), &mtp_count)) {
@@ -81,10 +94,10 @@ void pivot_and_umount(
     unex->count++;
 
     /* pivot_root */
-    if (chdir(old_place_for_new_root) < 0) {
-        strerr_diefu2sys(111, "chdir to ", old_place_for_new_root) ;
+    if (chdir(new_root) < 0) {
+        strerr_diefu2sys(111, "chdir to ", new_root) ;
     }
-    if (syscall_pivot_root(".", new_place_for_old_root) < 0) {
+    if (syscall_pivot_root(".", put_old) < 0) {
         strerr_diefu1sys(111, "pivot_root") ;
     }
     if (chroot(".") < 0) {
@@ -264,7 +277,17 @@ int main (int argc, char const *const *argv) {
     if (argc < 3) {
         dieusage();
     }
-    pivot_and_umount(argv[0], argv[1], &unex);
+    char *new_root = realpath(argv[0], NULL);
+    if (new_root == NULL) {
+	    strerr_diefu1sys(111, "to resolve first path");
+    }
+    char *put_old = realpath(argv[1], NULL);
+    if (new_root == NULL) {
+	    strerr_diefu1sys(111, "to resolve first path");
+    }
+    pivot_and_umount(new_root, put_old, &unex);
+    free(new_root);
+    free(put_old);
     if (drop_privs) {
         drop(&privs);
     } else if (seccomp_fd >= 0) {