ksud: su supports set gid and groups (#1240)

- When no gid is provided, use uid as gid.

userspace/ksud/src/ksu.rs

@@ -58,10 +58,12 @@ fn print_usage(program: &str, opts: Options) {
     print!("{}", opts.usage(&brief));
 }
 
-fn set_identity(uid: u32, gid: u32) {
+fn set_identity(uid: u32, gid: u32, groups: &Vec<u32>) {
     #[cfg(any(target_os = "linux", target_os = "android"))]
     unsafe {
-        libc::seteuid(uid);
+        if !groups.is_empty() {
+            libc::setgroups(groups.len(), groups.as_ptr());
+        }
         libc::setresgid(gid, gid, gid);
         libc::setresuid(uid, uid, uid);
     }
@@ -117,6 +119,13 @@ pub fn root_shell() -> Result<()> {
         "mount-master",
         "force run in the global mount namespace",
     );
+    opts.optopt("g", "group", "Specify the primary group", "GROUP");
+    opts.optmulti(
+        "G",
+        "supp-group",
+        "Specify a supplementary group. The first specified supplementary group is also used as a primary group if the option -g is not specified.",
+        "GROUP",
+    );
 
     // Replace -cn with -z, -mm with -M for supporting getopt_long
     let args = args
@@ -160,6 +169,31 @@ pub fn root_shell() -> Result<()> {
     let mut is_login = matches.opt_present("l");
     let preserve_env = matches.opt_present("p");
     let mount_master = matches.opt_present("M");
+    let mut groups = Vec::<u32>::new();
+    for g in matches.opt_strs("G") {
+        if let core::result::Result::Ok(id) = g.parse::<u32>() {
+            groups.push(id);
+        } else {
+            println!("Invalid GID: {g}");
+            print_usage(&program, opts);
+            return Ok(());
+        }
+    }
+    let mut gid: Option<u32> = None;
+    // if -g provided, use it.
+    if let Some(g) = matches.opt_str("g") {
+        if let core::result::Result::Ok(id) = g.parse::<u32>() {
+            gid = Some(id);
+        } else {
+            println!("Invalid GID: {g}");
+            print_usage(&program, opts);
+            return Ok(());
+        }
+    }
+    // otherwise, use the first gid of groups.
+    if gid.is_none() && !groups.is_empty() {
+        gid = Some(groups[0]);
+    }
 
     // we've make sure that -c is the last option and it already contains the whole command, no need to construct it again
     let args = matches
@@ -175,7 +209,6 @@ pub fn root_shell() -> Result<()> {
 
     // use current uid if no user specified, these has been done in kernel!
     let mut uid = unsafe { libc::getuid() };
-    let gid = unsafe { libc::getgid() };
     if free_idx < matches.free.len() {
         let name = &matches.free[free_idx];
         uid = unsafe {
@@ -191,6 +224,8 @@ pub fn root_shell() -> Result<()> {
         }
     }
 
+    // if there is no gid provided, use uid.
+    let gid = gid.unwrap_or(uid);
     // https://github.com/topjohnwu/Magisk/blob/master/native/src/su/su_daemon.cpp#L408
     let arg0 = if is_login { "-" } else { &shell };
 
@@ -241,7 +276,7 @@ pub fn root_shell() -> Result<()> {
                 let _ = utils::unshare_mnt_ns();
             }
 
-            set_identity(uid, gid);
+            set_identity(uid, gid, &groups);
 
             std::result::Result::Ok(())
         })