implement caps check for ptrace

Makefile

@@ -6,7 +6,7 @@ BIN_DIR				=	bin
 CC					=	gcc
 LD					=	ld
 CFLAGS				=	-Wall -I$(INC_DIR)
-LDFLAGS				=
+LDFLAGS				=	-lcap
 
 BLACKJACK_SRC		=	main.c process.c
 BLACKJACK_OBJ		:=	$(addprefix $(OBJ_DIR)/,$(patsubst %.c,%.o,$(BLACKJACK_SRC)))

include/process.h

@@ -52,4 +52,7 @@ int is_considered_active(process_state_t state);
 // find any active (running) thread and returns 0 and success, otherwise non zero
 int find_active_thread(process_status_t* list, size_t count, process_status_t** thread);
 
+// check if this process has any capability or is ran as root to be able to ptrace attach
+int check_ptrace_permissions();
+
 #endif

src/main.c

@@ -71,5 +71,13 @@ int main(int argc, char** argv)
 
     free(threads);
     free(list);
+
+    if (!check_ptrace_permissions())
+    {
+        fputs("this process doesn't have permission to ptrace.\n", stderr);
+        fputs("either run as root or set caps.\n", stderr);
+        return 1;
+    }
+    
     return 0;
 }

src/process.c

@@ -1,6 +1,7 @@
 #define _DEFAULT_SOURCE
 #include "process.h"
 #include "debug.h"
+#include <sys/capability.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <dirent.h>
@@ -212,3 +213,26 @@ int find_active_thread(process_status_t* list, size_t count, process_status_t**
     }
     return 1;
 }
+
+int check_ptrace_permissions()
+{
+    if (!geteuid())
+    {
+        // we're running as root
+        return 1;
+    }
+
+    // otherwise, check CAPS
+    cap_t cap = cap_get_pid(getpid());
+    cap_flag_value_t cap_flag_value;
+    
+    if (cap)
+    {
+        if (!cap_get_flag(cap, CAP_SYS_ADMIN, CAP_EFFECTIVE, &cap_flag_value))
+            if (cap_flag_value == CAP_SET) return 1;
+        if (!cap_get_flag(cap, CAP_SYS_ADMIN, CAP_PERMITTED, &cap_flag_value))
+            if (cap_flag_value == CAP_SET) return 1;
+    }
+
+    return 0;
+}