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Message-Id: <1562410493-8661-12-git-send-email-s.mesoraca16@gmail.com>
Date: Sat, 6 Jul 2019 12:54:52 +0200
From: Salvatore Mesoraca <s.mesoraca16@...il.com>
To: linux-kernel@...r.kernel.org
Cc: kernel-hardening@...ts.openwall.com,
linux-mm@...ck.org,
linux-security-module@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>,
Brad Spengler <spender@...ecurity.net>,
Casey Schaufler <casey@...aufler-ca.com>,
Christoph Hellwig <hch@...radead.org>,
James Morris <james.l.morris@...cle.com>,
Jann Horn <jannh@...gle.com>,
Kees Cook <keescook@...omium.org>,
PaX Team <pageexec@...email.hu>,
Salvatore Mesoraca <s.mesoraca16@...il.com>,
"Serge E. Hallyn" <serge@...lyn.com>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH v5 11/12] S.A.R.A.: /proc/*/mem write limitation
Prevent a task from opening, in "write" mode, any /proc/*/mem
file that operates on the task's mm.
A process could use it to overwrite read-only memory, bypassing
S.A.R.A. restrictions.
Signed-off-by: Salvatore Mesoraca <s.mesoraca16@...il.com>
---
security/sara/include/sara_data.h | 18 ++++++++++++++++-
security/sara/sara_data.c | 8 ++++++++
security/sara/wxprot.c | 41 +++++++++++++++++++++++++++++++++++++++
3 files changed, 66 insertions(+), 1 deletion(-)
diff --git a/security/sara/include/sara_data.h b/security/sara/include/sara_data.h
index 9216c47..ee95f74 100644
--- a/security/sara/include/sara_data.h
+++ b/security/sara/include/sara_data.h
@@ -15,6 +15,7 @@
#define __SARA_DATA_H
#include <linux/cred.h>
+#include <linux/fs.h>
#include <linux/init.h>
#include <linux/lsm_hooks.h>
#include <linux/spinlock.h>
@@ -40,6 +41,10 @@ struct sara_shm_data {
spinlock_t lock;
};
+struct sara_inode_data {
+ struct task_struct *task;
+};
+
static inline struct sara_data *get_sara_data(const struct cred *cred)
{
@@ -79,6 +84,17 @@ static inline struct sara_shm_data *get_sara_shm_data(
#define lock_sara_shm(X) (spin_lock(&get_sara_shm_data((X))->lock))
#define unlock_sara_shm(X) (spin_unlock(&get_sara_shm_data((X))->lock))
-#endif
+
+static inline struct sara_inode_data *get_sara_inode_data(
+ const struct inode *inode)
+{
+ if (unlikely(!inode->i_security))
+ return NULL;
+ return inode->i_security + sara_blob_sizes.lbs_inode;
+}
+
+#define get_sara_inode_task(X) (get_sara_inode_data((X))->task)
+
+#endif /* CONFIG_SECURITY_SARA_WXPROT */
#endif /* __SARA_H */
diff --git a/security/sara/sara_data.c b/security/sara/sara_data.c
index 9afca37..e875cf0 100644
--- a/security/sara/sara_data.c
+++ b/security/sara/sara_data.c
@@ -17,6 +17,7 @@
#include <linux/cred.h>
#include <linux/lsm_hooks.h>
#include <linux/mm.h>
+#include <linux/slab.h>
#include <linux/spinlock.h>
static int sara_cred_prepare(struct cred *new, const struct cred *old,
@@ -40,15 +41,22 @@ static int sara_shm_alloc_security(struct kern_ipc_perm *shp)
return 0;
}
+static void sara_task_to_inode(struct task_struct *t, struct inode *i)
+{
+ get_sara_inode_task(i) = t;
+}
+
static struct security_hook_list data_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(cred_prepare, sara_cred_prepare),
LSM_HOOK_INIT(cred_transfer, sara_cred_transfer),
LSM_HOOK_INIT(shm_alloc_security, sara_shm_alloc_security),
+ LSM_HOOK_INIT(task_to_inode, sara_task_to_inode),
};
struct lsm_blob_sizes sara_blob_sizes __lsm_ro_after_init = {
.lbs_cred = sizeof(struct sara_data),
.lbs_ipc = sizeof(struct sara_shm_data),
+ .lbs_inode = sizeof(struct sara_inode_data),
};
int __init sara_data_init(void)
diff --git a/security/sara/wxprot.c b/security/sara/wxprot.c
index 773d1fd..1a8d132 100644
--- a/security/sara/wxprot.c
+++ b/security/sara/wxprot.c
@@ -22,8 +22,11 @@
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/module.h>
+#include <linux/mount.h>
#include <linux/printk.h>
#include <linux/ratelimit.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
#include <linux/spinlock.h>
#include <linux/xattr.h>
@@ -615,6 +618,43 @@ static int sara_file_mprotect(struct vm_area_struct *vma,
return 0;
}
+static int sara_file_open(struct file *file)
+{
+ struct task_struct *t;
+ struct mm_struct *mm;
+ u16 sara_wxp_flags = get_current_sara_wxp_flags();
+
+ /*
+ * Prevent write access to /proc/.../mem
+ * if it operates on the mm_struct of the
+ * current process: it could be used to
+ * bypass W^X.
+ */
+
+ if (!sara_enabled ||
+ !wxprot_enabled ||
+ !(sara_wxp_flags & SARA_WXP_WXORX) ||
+ !(file->f_mode & FMODE_WRITE))
+ return 0;
+
+ t = get_sara_inode_task(file_inode(file));
+ if (unlikely(t != NULL &&
+ strcmp(file->f_path.dentry->d_name.name,
+ "mem") == 0)) {
+ get_task_struct(t);
+ mm = get_task_mm(t);
+ put_task_struct(t);
+ if (unlikely(mm == current->mm))
+ sara_warn_or_goto(error,
+ "write access to /proc/*/mem");
+ mmput(mm);
+ }
+ return 0;
+error:
+ mmput(mm);
+ return -EACCES;
+}
+
#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
static int sara_pagefault_handler(struct pt_regs *regs,
unsigned long error_code,
@@ -778,6 +818,7 @@ static int sara_setprocattr(const char *name, void *value, size_t size)
LSM_HOOK_INIT(check_vmflags, sara_check_vmflags),
LSM_HOOK_INIT(shm_shmat, sara_shm_shmat),
LSM_HOOK_INIT(file_mprotect, sara_file_mprotect),
+ LSM_HOOK_INIT(file_open, sara_file_open),
#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
LSM_HOOK_INIT(pagefault_handler, sara_pagefault_handler),
#endif
--
1.9.1
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