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Subject[PATCH v2 3/3] Wire UFFD up to SELinux
From
This change gives userfaultfd file descriptors a real security
context, allowing policy to act on them.

Signed-off-by: Daniel Colascione <dancol@google.com>
---
fs/userfaultfd.c | 34 +++++++++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 07b0f6e03849..78ff5d898733 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -76,6 +76,8 @@ struct userfaultfd_ctx {
bool mmap_changing;
/* mm with one ore more vmas attached to this userfaultfd_ctx */
struct mm_struct *mm;
+ /* The inode that owns this context --- not a strong reference. */
+ const struct inode *owner;
};

struct userfaultfd_fork_ctx {
@@ -1014,14 +1016,18 @@ 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,
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),
+ ctx->owner);
if (fd < 0)
return fd;

@@ -1918,7 +1924,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
}
#endif

-const struct file_operations userfaultfd_fops = {
+static const struct file_operations userfaultfd_fops = {
#ifdef CONFIG_PROC_FS
.show_fdinfo = userfaultfd_show_fdinfo,
#endif
@@ -1943,6 +1949,7 @@ static void init_once_userfaultfd_ctx(void *mem)

SYSCALL_DEFINE1(userfaultfd, int, flags)
{
+ struct file *file;
struct userfaultfd_ctx *ctx;
int fd;

@@ -1972,8 +1979,25 @@ 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));
+ file = anon_inode_getfile_secure(
+ "[userfaultfd]", &userfaultfd_fops, ctx,
+ O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS),
+ NULL);
+ if (IS_ERR(file)) {
+ fd = PTR_ERR(file);
+ goto out;
+ }
+
+ fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
+ if (fd < 0) {
+ fput(file);
+ goto out;
+ }
+
+ ctx->owner = file_inode(file);
+ fd_install(fd, file);
+
+out:
if (fd < 0) {
mmdrop(ctx->mm);
kmem_cache_free(userfaultfd_ctx_cachep, ctx);
--
2.25.1.696.g5e7596f4ac-goog
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