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Date: Sun, 7 Aug 2011 15:00:25 +0400
From: Vasiliy Kulikov <segoon@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Cc: Will Drewry <wad@...omium.org>
Subject: 32/64 bitness restriction for pid namespace
Solar, Will, all -
The new sysctl is introduced, abi.bitness_locked. If set to 1, it locks
all tasks inside of current pid namespace to the bitness of init task
(pid_ns->child_reaper). After that (1) all syscalls of other bitness
return -ENOSYS and (2) loading ELF binaries of another bitness is
prohibited (as if the corresponding CONFIG_BINFMT_*=N). If there is any
task which differs in bitness, the lockup fails.
TODO:
* Fix a race of sysctl against fork().
* Denied syscall should behave as if it doesn't exist.
The patch was tested very roughly.
diff --git a/arch/x86/kernel/syscall_restrict.c b/arch/x86/kernel/syscall_restrict.c
index 1a2bf1c..b2bfd8f 100644
--- a/arch/x86/kernel/syscall_restrict.c
+++ b/arch/x86/kernel/syscall_restrict.c
@@ -31,8 +31,8 @@ static int task_get_bitness(struct task_struct *task)
static bool pidns_locked(struct pid_namespace *pid_ns)
{
struct task_struct *init = pid_ns->child_reaper;
- return (test_ti_thread_flag(task_thread_info(task), TIF_SYSCALL32_DENIED) ||
- test_ti_thread_flag(task_thread_info(task), TIF_SYSCALL64_DENIED));
+ return (test_ti_thread_flag(task_thread_info(init), TIF_SYSCALL32_DENIED) ||
+ test_ti_thread_flag(task_thread_info(init), TIF_SYSCALL64_DENIED));
}
static int bits_to_flags(int bits)
@@ -69,7 +69,7 @@ static int __pidns_may_lock_bitness(struct pid_namespace *pid_ns, int bits)
}
/* Called with hold tasklist_lock and rcu */
-static int __change_syscall_restrict(struct pid_namespace *pid_ns, int bits)
+static int __bitness_lock(struct pid_namespace *pid_ns, int bits)
{
u32 clear_bit_nr;
struct task_struct *p, *thread;
@@ -90,7 +90,7 @@ static int __change_syscall_restrict(struct pid_namespace *pid_ns, int bits)
return 0;
}
-static int syscall_bitness_lock(struct pid_namespace *pid_ns)
+static int bitness_lock(struct pid_namespace *pid_ns)
{
int rc, new_bits;
@@ -100,14 +100,14 @@ static int syscall_bitness_lock(struct pid_namespace *pid_ns)
new_bits = task_get_bitness(pid_ns->child_reaper);
rc = __pidns_may_lock_bitness(pid_ns, new_bits);
if (!rc)
- rc = __change_syscall_restrict(pid_ns, new_bits);
+ rc = __bitness_lock(pid_ns, new_bits);
write_unlock_irq(&tasklist_lock);
rcu_read_unlock();
return rc;
}
-static int syscall_bitness_locked_handler(struct ctl_table *table, int write,
+static int bitness_locked_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
@@ -128,14 +128,14 @@ static int syscall_bitness_locked_handler(struct ctl_table *table, int write,
return -EACCES;
if (new_bits && old_bits)
return 0;
- return syscall_bitness_lock(current->nsproxy->pid_ns);
+ return bitness_lock(current->nsproxy->pid_ns);
}
static struct ctl_table abi_syscall_restrict[] = {
{
- .procname = "syscall_bitness_locked",
+ .procname = "bitness_locked",
.mode = 0644,
- .proc_handler = syscall_bitness_locked_handler
+ .proc_handler = bitness_locked_handler
},
{}
};
---
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