[PATCH v9 3/3] Wire UFFD up to SELinux

From: Lokesh Gidra
Date: Wed Sep 23 2020 - 15:33:52 EST


From: Daniel Colascione <dancol@xxxxxxxxxx>

This change gives userfaultfd file descriptors a real security
context, allowing policy to act on them.

Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>

[Remove owner inode from userfaultfd_ctx]
[Use anon_inode_getfd_secure() instead of anon_inode_getfile_secure()
in userfaultfd syscall]
[Use inode of file in userfaultfd_read() in resolve_userfault_fork()]

Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
---
fs/userfaultfd.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 0e4a3837da52..918535b49475 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -978,14 +978,14 @@ static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)

static const struct file_operations userfaultfd_fops;

-static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
- struct userfaultfd_ctx *new,
+static int resolve_userfault_fork(struct userfaultfd_ctx *new,
+ struct inode *inode,
struct uffd_msg *msg)
{
int fd;

- fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
- O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
+ fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
+ O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
if (fd < 0)
return fd;

@@ -995,7 +995,7 @@ static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
}

static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
- struct uffd_msg *msg)
+ struct uffd_msg *msg, struct inode *inode)
{
ssize_t ret;
DECLARE_WAITQUEUE(wait, current);
@@ -1106,7 +1106,7 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
spin_unlock_irq(&ctx->fd_wqh.lock);

if (!ret && msg->event == UFFD_EVENT_FORK) {
- ret = resolve_userfault_fork(ctx, fork_nctx, msg);
+ ret = resolve_userfault_fork(fork_nctx, inode, msg);
spin_lock_irq(&ctx->event_wqh.lock);
if (!list_empty(&fork_event)) {
/*
@@ -1166,6 +1166,7 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
ssize_t _ret, ret = 0;
struct uffd_msg msg;
int no_wait = file->f_flags & O_NONBLOCK;
+ struct inode *inode = file_inode(file);

if (ctx->state == UFFD_STATE_WAIT_API)
return -EINVAL;
@@ -1173,7 +1174,7 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
for (;;) {
if (count < sizeof(msg))
return ret ? ret : -EINVAL;
- _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
+ _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
if (_ret < 0)
return ret ? ret : _ret;
if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
@@ -1995,8 +1996,8 @@ SYSCALL_DEFINE1(userfaultfd, int, flags)
/* prevent the mm struct to be freed */
mmgrab(ctx->mm);

- fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
- O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
+ fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
+ O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
if (fd < 0) {
mmdrop(ctx->mm);
kmem_cache_free(userfaultfd_ctx_cachep, ctx);
--
2.28.0.681.g6f77f65b4e-goog