From 49ebe01635805b8f383c96556ba38a7f9b7ba3dd Mon Sep 17 00:00:00 2001
From: Sapan Bhatia <gwsapan@gmail.com>
Date: Mon, 17 Sep 2012 06:56:04 -0400
Subject: [PATCH] Fixed bad security loophole in write path

---
 Makefile      |   2 +-
 procprotect.c | 302 ++++++++++++++++++++++++++++----------------------
 2 files changed, 172 insertions(+), 132 deletions(-)

diff --git a/Makefile b/Makefile
index a328711..8dfd78e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 obj-m += procprotect.o
 
 all:
-	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+	make -C /lib/modules/3.4.9-2.fc16.x86_64/build M=$(PWD) modules
 
 clean:
 	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
diff --git a/procprotect.c b/procprotect.c
index d49a41b..c1c0162 100644
--- a/procprotect.c
+++ b/procprotect.c
@@ -45,12 +45,13 @@ MODULE_LICENSE("GPL");
 MODULE_VERSION(VERSION_STR);
 
 struct procprotect_ctx {
-	struct inode **inode;
+    struct inode **inode;
+    int flags;
 };
 
 struct acl_entry {
-	unsigned int ino;
-	struct hlist_node hlist;
+    unsigned int ino;
+    struct hlist_node hlist;
 };
 
 #define HASH_SIZE (1<<16)
@@ -60,166 +61,205 @@ struct hlist_head procprotect_hash[HASH_SIZE];
 struct proc_dir_entry *proc_entry;
 
 /*
-  Entry point of intercepted call. We need to do two things here:
-  - Decide if we need the heavier return hook to be called
-  - Save the first argument, which is in a register, for consideration in the return hook
-*/
+   Entry point of intercepted call. We need to do two things here:
+   - Decide if we need the heavier return hook to be called
+   - Save the first argument, which is in a register, for consideration in the return hook
+   */
 static int do_lookup_entry(struct kretprobe_instance *ri, struct pt_regs *regs) {
-	int ret = -1;
-	struct procprotect_ctx *ctx;
-	struct nameidata *nd = (struct nameidata *) regs->di;
-	struct qstr *q = (struct qstr *) regs->si;
-	struct dentry *parent = nd->path.dentry;
-	struct inode *pinode = parent->d_inode;
-	
-	if (pinode->i_sb->s_magic == PROC_SUPER_MAGIC) {	
-		ctx = (struct procprotect_ctx *) ri->data;
-		ctx->inode = (struct inode **) regs->cx;
-		ret = 0;
-	}
-
-	return ret;
+    int ret = -1;
+    struct procprotect_ctx *ctx;
+    struct nameidata *nd = (struct nameidata *) regs->di;
+    struct qstr *q = (struct qstr *) regs->si;
+    struct dentry *parent = nd->path.dentry;
+    struct inode *pinode = parent->d_inode;
+
+    if (pinode->i_sb->s_magic == PROC_SUPER_MAGIC
+            && current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns) {	
+        ctx = (struct procprotect_ctx *) ri->data;
+        ctx->inode = regs->cx;
+        ctx->flags = nd->flags;
+        ret = 0;
+    }
+
+    return ret;
 }
 
 static int run_acl(unsigned long ino) {
-	struct hlist_node *n;
-	struct acl_entry *entry;
-	hlist_for_each_entry_rcu(entry, 
-		n, &procprotect_hash[ino & (HASH_SIZE-1)],
-		hlist) {
-		if (entry->ino==ino) {
-			return 0;
-		}
-	}
-	return 1;
+    struct hlist_node *n;
+    struct acl_entry *entry;
+    hlist_for_each_entry_rcu(entry, 
+            n, &procprotect_hash[ino & (HASH_SIZE-1)],
+            hlist) {
+        if (entry->ino==ino) {
+            return 0;
+        }
+    }
+    return 1;
 }
 
 /* The entry hook ensures that the return hook is only called for
-accesses to /proc */
+   accesses to /proc */
 
 static int do_lookup_ret(struct kretprobe_instance *ri, struct pt_regs *regs)
 {
-	struct procprotect_ctx *ctx = (struct procprotect_ctx *) ri->data;
-	int ret = regs->ax;
-	
-	if (ret==0) {
-		/* The kernel is going to honor the request. Here's where we step in */
-		struct inode *inode = *(ctx->inode);
-		//printk(KERN_CRIT "Checking inode %x number %u",inode,inode->i_ino);
-		if (!run_acl(inode->i_ino)) {
-			if (current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns)
-				regs->ax = -EPERM;
-		}
-	}
-	
-	return 0;
+    struct procprotect_ctx *ctx = (struct procprotect_ctx *) ri->data;
+    int ret = regs->ax;
+
+    if (ret==0) {
+        /* The kernel is going to honor the request. Here's where we step in */
+        struct inode *inode = *(ctx->inode);
+        if (!run_acl(inode->i_ino)) {
+            if (current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns) {
+                regs->ax = -EPERM;
+            }
+        }
+    }
+
+    return 0;
 }
 
+struct open_flags {
+  int open_flag;
+  umode_t mode;
+  int acc_mode;
+  int intent;
+};
+
+static struct file *do_last_probe(struct nameidata *nd, struct path *path,
+                         struct open_flags *op, const char *pathname) {
+    struct dentry *parent = nd->path.dentry;
+    struct inode *pinode = parent->d_inode;
+
+    if (pinode->i_sb->s_magic == PROC_SUPER_MAGIC && current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns) {
+        op->open_flag &= ~O_CREAT;
+    }
+    jprobe_return();
+}
+
+static struct jprobe dolast_probe = {
+	.entry = (kprobe_opcode_t *) do_last_probe
+};
+
 static struct kretprobe proc_probe = {
-	.entry_handler = (kprobe_opcode_t *) do_lookup_entry,
-        .handler = (kprobe_opcode_t *) do_lookup_ret,
-	.maxactive = 20,
-	.data_size = sizeof(struct procprotect_ctx)
+    .entry_handler = (kprobe_opcode_t *) do_lookup_entry,
+    .handler = (kprobe_opcode_t *) do_lookup_ret,
+    .maxactive = 20,
+    .data_size = sizeof(struct procprotect_ctx)
 };
 
 static void add_entry(char *pathname) {
-	struct path path;
-	if (kern_path(pathname, 0, &path)) {
-		printk(KERN_CRIT "Path lookup failed for %s",pathname);
-	}	
-	else {
-		unsigned int ino = path.dentry->d_inode->i_ino;
-		struct acl_entry *entry;
-		entry = kmalloc(GFP_KERNEL, sizeof(struct acl_entry));
-		entry->ino = ino;
-		
-		if (!entry) {
-			printk(KERN_CRIT "Could not allocate memory for %s",pathname);
-		}
-		else {
-			if (run_acl(ino)) {
-				hlist_add_head_rcu(&entry->hlist,&procprotect_hash[ino&(HASH_SIZE-1)]);
-				printk(KERN_CRIT "Added inode %u",ino);
-			}
-			else {
-				printk(KERN_CRIT "Did not add inode %u, already in list", ino);
-			}
-		}
-	}
+    struct path path;
+    if (kern_path(pathname, 0, &path)) {
+        printk(KERN_CRIT "Path lookup failed for %s",pathname);
+    }	
+    else {
+        unsigned int ino = path.dentry->d_inode->i_ino;
+        struct acl_entry *entry;
+        entry = kmalloc(GFP_KERNEL, sizeof(struct acl_entry));
+        entry->ino = ino;
+
+        if (!entry) {
+            printk(KERN_CRIT "Could not allocate memory for %s",pathname);
+        }
+        else {
+            if (run_acl(ino)) {
+                hlist_add_head_rcu(&entry->hlist,&procprotect_hash[ino&(HASH_SIZE-1)]);
+                printk(KERN_CRIT "Added inode %u",ino);
+            }
+            else {
+                printk(KERN_CRIT "Did not add inode %u, already in list", ino);
+            }
+        }
+    }
 }
 
 
 static void __exit procprotect_exit(void)
 {
-	unregister_kretprobe(&proc_probe);
-	struct hlist_node *n;
-	struct acl_entry *entry;
-	int i;
-
-	for (i=0;i<HASH_SIZE;i++) {
-		hlist_for_each_entry_rcu(entry, 
-			n, &procprotect_hash[i],
-			hlist) {
-				kfree(entry);
-		}
-	}
-	
-	remove_proc_entry("procprotect",NULL);
-	printk("Procprotect: Stopped procprotect.\n");
+    unregister_kretprobe(&proc_probe);
+	unregister_jprobe(&dolast_probe);
+    struct hlist_node *n;
+    struct acl_entry *entry;
+    int i;
+
+    for (i=0;i<HASH_SIZE;i++) {
+        hlist_for_each_entry_rcu(entry, 
+                n, &procprotect_hash[i],
+                hlist) {
+            kfree(entry);
+        }
+    }
+
+    remove_proc_entry("procprotect",NULL);
+    printk("Procprotect: Stopped procprotect.\n");
 }
 
 
 
 int procfile_write(struct file *file, const char *buffer, unsigned long count, void *data) {		
-	char pathname[PATH_MAX];
-
-	if (current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns)
-		return -EPERM;
-
-	if (copy_from_user(pathname, buffer, count)) {
-		return -EFAULT;
-	}
-	if (count && (pathname[count-1]==10 || pathname[count-1]==13)) {
-		pathname[count-1]='\0';
-	}
-	else
-		pathname[count]='\0';
-	add_entry(pathname);	
-	printk(KERN_CRIT "Length of buffer=%d",strlen(pathname));
-	return count;
+    char pathname[PATH_MAX];
+
+    if (current->nsproxy->mnt_ns!=init_task.nsproxy->mnt_ns)
+        return -EPERM;
+
+    if (copy_from_user(pathname, buffer, count)) {
+        return -EFAULT;
+    }
+    if (count && (pathname[count-1]==10 || pathname[count-1]==13)) {
+        pathname[count-1]='\0';
+    }
+    else
+        pathname[count]='\0';
+    add_entry(pathname);	
+    printk(KERN_CRIT "Length of buffer=%d",strlen(pathname));
+    return count;
 }
 
 static int __init procprotect_init(void)
 {
-	printk("Procprotect: starting procprotect version %s with ACLs at path %s.\n",
-	       VERSION_STR, aclpath);
-	int ret;
-	int i;
-
-	for(i=0;i<HASH_SIZE;i++) {
-		INIT_HLIST_HEAD(&procprotect_hash[i]);
-	}
-
-	  aclqpath.name = aclpath;
-	  aclqpath.len = strnlen(aclpath, PATH_MAX);
-
-          proc_probe.kp.addr = 
-                  (kprobe_opcode_t *) kallsyms_lookup_name("do_lookup");
-          if (!proc_probe.kp.addr) {
-                  printk("Couldn't find %s to plant kretprobe\n", "do_execve");
-                  return -1;
-          }
-  
-          if ((ret = register_kretprobe(&proc_probe)) <0) {
-                  printk("register_kretprobe failed, returned %d\n", ret);
+    printk("Procprotect: starting procprotect version %s with ACLs at path %s.\n",
+            VERSION_STR, aclpath);
+    int ret;
+    int i;
+
+    for(i=0;i<HASH_SIZE;i++) {
+        INIT_HLIST_HEAD(&procprotect_hash[i]);
+    }
+
+    aclqpath.name = aclpath;
+    aclqpath.len = strnlen(aclpath, PATH_MAX);
+
+    proc_probe.kp.addr = 
+        (kprobe_opcode_t *) kallsyms_lookup_name("do_lookup");
+    if (!proc_probe.kp.addr) {
+        printk("Couldn't find %s to plant kretprobe\n", "do_execve");
+        return -1;
+    }
+
+    dolast_probe.kp.addr = 
+        (kprobe_opcode_t *) kallsyms_lookup_name("do_last");
+
+    if (!dolast_probe.kp.addr) {
+        printk("Couldn't find %s to plant kretprobe\n", "do_last");
+        return -1;
+    }
+
+    if ((ret = register_jprobe(&dolast_probe)) <0) {
+                  printk("register_jprobe failed, returned %u\n", ret);
                   return -1;
-          }
-          printk("Planted kretprobe at %p, handler addr %p\n",
-                 proc_probe.kp.addr, proc_probe.handler);
+    }
+
+    if ((ret = register_kretprobe(&proc_probe)) <0) {
+        printk("register_kretprobe failed, returned %d\n", ret);
+        return -1;
+    }
+    printk("Planted kretprobe at %p, handler addr %p\n",
+            proc_probe.kp.addr, proc_probe.handler);
+
+    proc_entry = create_proc_entry("procprotect", 0644, NULL);
+    proc_entry->write_proc = procfile_write;
 
-	proc_entry = create_proc_entry("procprotect", 0644, NULL);
-	proc_entry->write_proc = procfile_write;
-        return ret;
+    return ret;
 }
 
 
-- 
2.43.0