non-dumpable plugins

(hopefully) fixes the issues that led to reverting
commits 6abb65d328af61d67361890743190bd4c57f8e3c and 98e42dc6da4e4b1e47ed2aa020012d4dedc1e80e

1 files changed, 33 insertions, 1 deletions

diff --git a/src/lib/common.c b/src/lib/common.c
index 823442835..ace5cb87e 100644
--- a/src/lib/common.c
+++ b/src/lib/common.c
@@ -267,7 +267,6 @@ int pid_proc_cmdline_x11_xpra_xephyr(const pid_t pid) {
 }
 
 // return 1 if /proc is mounted hidepid, or if /proc/mouns access is denied
-#define BUFLEN 4096
 int pid_hidepid(void) {
         FILE *fp = fopen("/proc/mounts", "r");
         if (!fp)
@@ -288,6 +287,39 @@ int pid_hidepid(void) {
         return 0;
 }
 
+// print error if unprivileged users can trace the process
+void warn_dumpable(void) {
+        if (getuid() != 0 && prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 1 && getenv("FIREJAIL_PLUGIN")) {
+                fprintf(stderr, "Error: dumpable process\n");
+
+                // best effort to provide detailed debug information
+                // cannot use process name, it is just a file descriptor number
+                char path[BUFLEN];
+                ssize_t len = readlink("/proc/self/exe", path, BUFLEN - 1);
+                if (len < 0)
+                        return;
+                path[len] = '\0';
+                // path can refer to a sandbox mount namespace, use basename only
+                const char *base = gnu_basename(path);
+
+                struct stat s;
+                if (stat("/proc/self/exe", &s) == 0 && s.st_uid != 0)
+                        fprintf(stderr, "Change owner of %s executable to root\n", base);
+                else if (access("/proc/self/exe", R_OK) == 0)
+                        fprintf(stderr, "Remove read permission on %s executable\n", base);
+        }
+}
+
+// Equivalent to the GNU version of basename, which is incompatible with
+// the POSIX basename. A few lines of code saves any portability pain.
+// https://www.gnu.org/software/libc/manual/html_node/Finding-Tokens-in-a-String.html#index-basename
+const char *gnu_basename(const char *path) {
+        const char *last_slash = strrchr(path, '/');
+        if (!last_slash)
+                return path;
+        return last_slash+1;
+}
+
 //**************************
 // time trace based on getticks function
 //**************************