From f1fd55d06bc3660a784d0af5af9b3e2459184c04 Mon Sep 17 00:00:00 2001
From: Trung <trung_bao.d@kbtgvn.tech>
Date: Fri, 17 Jul 2026 12:25:42 +0700
Subject: [PATCH] sysroot bypass hardcoded /etc/passwd and /etc/group
 intercepts

When a custom guest sysroot is configured, hardcoded intercepts on
/etc/passwd and /etc/group shadow the actual files in the guest rootfs.
This prevents guest processes from resolving users and groups that
were added during package provisioning.

We now check if a sysroot is active in path_might_use_open_intercept()
and bypass the synthetic intercepts in that case, allowing the guest
to read the actual user/group database from its rootfs.

Fix #188
---
 mk/tests.mk                        |  2 ++
 src/syscall/path.c                 | 16 ++++++++++++++--
 tests/test-sysroot-host-fallback.c | 16 ++++++++++++++++
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/mk/tests.mk b/mk/tests.mk
index 85c3e456..5f07a44c 100644
--- a/mk/tests.mk
+++ b/mk/tests.mk
@@ -257,6 +257,8 @@ test-sysroot-host-fallback: $(ELFUSE_BIN) $(BUILD_DIR)/test-sysroot-host-fallbac
 	printf 'host-final\n' > "$$mirror/final.txt"; \
 	printf 'host-loses\n' > "$$mirror/both.txt"; \
 	printf 'sysroot-wins\n' > "$$sysroot$$mirror/both.txt"; \
+	mkdir -p "$$sysroot/etc"; \
+	printf 'guest-passwd\n' > "$$sysroot/etc/passwd"; \
 	$(ELFUSE_BIN) --sysroot "$$sysroot" \
 	    $(BUILD_DIR)/test-sysroot-host-fallback \
 	    "$$hostdir" "$$mirror/final.txt" "$$mirror/both.txt"
diff --git a/src/syscall/path.c b/src/syscall/path.c
index 2888a023..46a7053a 100644
--- a/src/syscall/path.c
+++ b/src/syscall/path.c
@@ -56,9 +56,21 @@ bool path_might_use_open_intercept(const char *path)
         return true;
     if (path_prefix_match(path, SYSFS_CPU_PREFIX, sizeof(SYSFS_CPU_PREFIX) - 1))
         return true;
-    if (!strcmp(path, "/etc/mtab") || !strcmp(path, "/etc/passwd") ||
-        !strcmp(path, "/etc/group"))
+    if (!strcmp(path, "/etc/mtab"))
         return true;
+    if (!strcmp(path, "/etc/passwd") || !strcmp(path, "/etc/group")) {
+        char sr[LINUX_PATH_MAX];
+        if (proc_sysroot_snapshot(sr, sizeof(sr))) {
+            char sysroot_file[LINUX_PATH_MAX];
+            if (snprintf(sysroot_file, sizeof(sysroot_file), "%s%s", sr, path) <
+                (int) sizeof(sysroot_file)) {
+                struct stat st;
+                if (stat(sysroot_file, &st) == 0)
+                    return false;
+            }
+        }
+        return true;
+    }
     if (!strcmp(path, "/var/run/utmp") || !strcmp(path, "/run/utmp"))
         return true;
 
diff --git a/tests/test-sysroot-host-fallback.c b/tests/test-sysroot-host-fallback.c
index 3f4119cb..27c6d0cd 100644
--- a/tests/test-sysroot-host-fallback.c
+++ b/tests/test-sysroot-host-fallback.c
@@ -133,6 +133,22 @@ int main(int argc, char **argv)
     else
         PASS();
 
+    TEST("sysroot passwd file wins over synthetic intercept");
+    if (read_file_nul("/etc/passwd", buf, sizeof(buf)) <= 0)
+        FAIL("read /etc/passwd failed");
+    else if (strcmp(buf, "guest-passwd\n"))
+        FAIL("did not bypass /etc/passwd synthetic intercept");
+    else
+        PASS();
+
+    TEST("absent sysroot group file falls back to synthetic intercept");
+    if (read_file_nul("/etc/group", buf, sizeof(buf)) <= 0)
+        FAIL("read /etc/group failed");
+    else if (strncmp(buf, "root:x:0:\nstaff:x:20:\nuser:x:1000:\n", 32))
+        FAIL("did not fall back to synthetic group intercept");
+    else
+        PASS();
+
     SUMMARY("test-sysroot-host-fallback");
     return fails > 0 ? 1 : 0;
 }