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Subject[PATCH 10/11] capsicum: prctl(2) to force use of O_BENEATH
Date
Add a per-task flag that indicates all openat(2) operations
should implicitly have the O_BENEATH flag set.

Add a prctl(2) command to set this flag (irrevocably). Include
an option to force the flag set to be synchronized across all
tasks in the thread group.

Signed-off-by: David Drysdale <drysdale@google.com>
---
fs/namei.c | 3 +++
include/linux/sched.h | 3 +++
include/uapi/linux/prctl.h | 14 ++++++++++++++
kernel/sys.c | 28 ++++++++++++++++++++++++++++
4 files changed, 48 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index fe03a7dd7537..5d3b440869df 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1849,6 +1849,9 @@ static int path_init(int dfd, const char *name, unsigned int *flags,
nd->flags = (*flags) | LOOKUP_PARENT | LOOKUP_JUMPED;
nd->depth = 0;

+ if (current->openat_beneath)
+ *flags |= LOOKUP_BENEATH;
+
if ((*flags) & LOOKUP_ROOT) {
struct dentry *root = nd->root.dentry;
struct inode *inode = root->d_inode;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 306f4f0c987a..8d2943879b7b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1303,6 +1303,9 @@ struct task_struct {
/* Used for emulating ABI behavior of previous Linux versions */
unsigned int personality;

+ /* Indicate that openat(2) operations implictly have O_BENEATH */
+ unsigned openat_beneath:1;
+
unsigned in_execve:1; /* Tell the LSMs that the process is doing an
* execve */
unsigned in_iowait:1;
diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 58afc04c107e..b34fb2bbdaf8 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -152,4 +152,18 @@
#define PR_SET_THP_DISABLE 41
#define PR_GET_THP_DISABLE 42

+/*
+ * If openat_beneath is set for a task, then all openat(2) operations will
+ * implicitly have the O_BENEATH flag set for them. Once set, this flag cannot
+ * be cleared.
+ */
+#define PR_SET_OPENAT_BENEATH 44
+#define PR_GET_OPENAT_BENEATH 45
+
+/*
+ Indicate that the openat_beneath flag should be synchronized across all
+ * threads in the process.
+ */
+#define PR_SET_OPENAT_BENEATH_TSYNC 0x01
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 8d8ccf6cfb38..cf2530c41982 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1821,6 +1821,23 @@ out:
return error;
}

+static int prctl_set_openat_beneath(struct task_struct *me, unsigned long flags)
+{
+ me->openat_beneath = 1;
+ if (flags & PR_SET_OPENAT_BENEATH_TSYNC) {
+ struct task_struct *thread, *caller;
+ unsigned long tflags;
+
+ write_lock_irqsave(&tasklist_lock, tflags);
+ thread = caller = me;
+ while_each_thread(caller, thread) {
+ thread->openat_beneath = 1;
+ }
+ write_unlock_irqrestore(&tasklist_lock, tflags);
+ }
+ return 0;
+}
+
#ifdef CONFIG_CHECKPOINT_RESTORE
static int prctl_get_tid_address(struct task_struct *me, int __user **tid_addr)
{
@@ -1996,6 +2013,17 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
return current->no_new_privs ? 1 : 0;
+ case PR_SET_OPENAT_BENEATH:
+ if (arg2 != 1 || arg4 || arg5)
+ return -EINVAL;
+ if ((arg3 & ~(PR_SET_OPENAT_BENEATH_TSYNC)) != 0)
+ return -EINVAL;
+ error = prctl_set_openat_beneath(me, arg3);
+ break;
+ case PR_GET_OPENAT_BENEATH:
+ if (arg2 || arg3 || arg4 || arg5)
+ return -EINVAL;
+ return me->openat_beneath;
case PR_GET_THP_DISABLE:
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
--
2.0.0.526.g5318336


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