fix suid config handling

2 files changed, 27 insertions, 16 deletions

diff --git a/applets/applets.c b/applets/applets.c
index 66bcc42de..32c63d1e0 100644
--- a/applets/applets.c
+++ b/applets/applets.c
@@ -110,9 +110,6 @@ static char *get_trimmed_slice(char *s, char *e)
 /* Don't depend on the tools to combine strings. */
 static const char config_file[] = "/etc/busybox.conf";
 
-/* There are 4 chars + 1 nul for each of user/group/other. */
-static const char mode_chars[] = "Ssx-\0Ssx-\0Ttx-";
-
 /* We don't supply a value for the nul, so an index adjustment is
  * necessary below.  Also, we use unsigned short here to save some
  * space even though these are really mode_t values. */
@@ -257,6 +254,9 @@ static void parse_config_file(void)
                                 e = skip_whitespace(e+1);
 
                                 for (i = 0; i < 3; i++) {
+                                        /* There are 4 chars + 1 nul for each of user/group/other. */
+                                        static const char mode_chars[] = "Ssx-\0" "Ssx-\0" "Ttx-";
+
                                         const char *q;
                                         q = strchrnul(mode_chars + 5*i, *e++);
                                         if (!*q) {
@@ -337,7 +337,8 @@ static inline void parse_config_file(void)
 #if ENABLE_FEATURE_SUID
 static void check_suid(const struct bb_applet *applet)
 {
-        uid_t rgid;  /* real gid */
+        uid_t uid;
+        gid_t rgid;  /* real gid */
 
         if (ruid == 0) /* set by parse_config_file() */
                 return; /* run by root - no need to check more */
@@ -368,16 +369,24 @@ static void check_suid(const struct bb_applet *applet)
                 if (!(m & S_IXOTH))           /* is x bit not set ? */
                         bb_error_msg_and_die("you have no permission to run this applet!");
 
-                if (sct->m_gid != 0) {
-                        /* _both_ have to be set for sgid */
-                        if ((sct->m_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
-                                xsetgid(sct->m_gid);
-                        } else xsetgid(rgid); /* no sgid -> drop */
-                }
-                if (sct->m_uid != 0) {
-                        if (sct->m_mode & S_ISUID) xsetuid(sct->m_uid);
-                        else xsetuid(ruid); /* no suid -> drop */
-                }
+                /* _both_ sgid and group_exec have to be set for setegid */
+                if ((sct->m_mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP))
+                        rgid = sct->m_gid;
+                /* else (no setegid) we will set egid = rgid */
+
+                /* We set effective AND saved ids. If saved-id is not set
+                 * like we do below, seteiud(0) can still later succeed! */
+                if (setresgid(-1, rgid, rgid))
+                        bb_perror_msg_and_die("setresgid");
+
+                /* do we have to set effective uid? */
+                uid = ruid;
+                if (sct->m_mode & S_ISUID)
+                        uid = sct->m_uid;
+                /* else (no seteuid) we will set euid = ruid */
+
+                if (setresuid(-1, uid, uid))
+                        bb_perror_msg_and_die("setresuid");
                 return;
         }
 #if !ENABLE_FEATURE_SUID_CONFIG_QUIET
@@ -393,6 +402,8 @@ static void check_suid(const struct bb_applet *applet)
 #endif
 
         if (applet->need_suid == _BB_SUID_ALWAYS) {
+                /* Real uid is not 0. If euid isn't 0 too, suid bit
+                 * is most probably not set on our executable */
                 if (geteuid())
                         bb_error_msg_and_die("applet requires root privileges!");
         } else if (applet->need_suid == _BB_SUID_NEVER) {
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index 7e1109470..a85a046cf 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -386,13 +386,13 @@ char *bin2hex(char *p, const char *cp, int count)
 // setgid() will fail and we'll _still_be_root_, which is bad.)
 void xsetgid(gid_t gid)
 {
-        if (setgid(gid)) bb_error_msg_and_die("setgid");
+        if (setgid(gid)) bb_perror_msg_and_die("setgid");
 }
 
 // Die with an error message if we can't set uid.  (See xsetgid() for why.)
 void xsetuid(uid_t uid)
 {
-        if (setuid(uid)) bb_error_msg_and_die("setuid");
+        if (setuid(uid)) bb_perror_msg_and_die("setuid");
 }
 
 // Return how long the file at fd is, if there's any way to determine it.