Re: [PATCH v5 3/3] Wire UFFD up to SELinux
From: Eric Biggers <ebiggers@kernel.org>
Date: 2020-08-04 21:16:15
Also in:
kvm, linux-fsdevel, lkml, selinux
On Wed, Apr 01, 2020 at 02:39:03PM -0700, Daniel Colascione wrote:
quoted hunk ↗ jump to hunk
This change gives userfaultfd file descriptors a real security context, allowing policy to act on them. Signed-off-by: Daniel Colascione <redacted> --- fs/userfaultfd.c | 30 ++++++++++++++++++++++++++---- 1 file changed, 26 insertions(+), 4 deletions(-)diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 37df7c9eedb1..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; };
Adding this field seems wrong. There's no reference held to it, so it can only be used if the caller holds a reference to the inode anyway. The only user of this field is via userfafultfd_read(), so why not just use the inode of the struct file passed to userfaultfd_read()?
quoted hunk ↗ jump to hunk
SYSCALL_DEFINE1(userfaultfd, int, flags) { + struct file *file; struct userfaultfd_ctx *ctx; int fd;@@ -1974,8 +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);
What's the point of anon_inode_getfile_secure()? anon_inode_getfd_secure() would work here too. - Eric