fs: consistently use can_mmap_file() helper

Since commit c84bf6d ("mm: introduce new .mmap_prepare() file
callback"), the f_op->mmap() hook has been deprecated in favour of
f_op->mmap_prepare().

Additionally, commit bb666b7 ("mm: add mmap_prepare() compatibility
layer for nested file systems") permits the use of the .mmap_prepare() hook
even in nested filesystems like overlayfs.

There are a number of places where we check only for f_op->mmap - this is
incorrect now mmap_prepare exists, so update all of these to use the
general helper can_mmap_file().

Most notably, this updates the elf logic to allow for the ability to
execute binaries on filesystems which have the .mmap_prepare hook, but
additionally we update nested filesystems.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/b68145b609532e62bab603dd9686faa6562046ec.1750099179.git.lorenzo.stoakes@oracle.com
Acked-by: Kees Cook <kees@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: ljskernel

fs/backing-file.c

@@ -333,7 +333,7 @@ int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
 	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
 		return -EIO;
 
-	if (!file->f_op->mmap)
+	if (!can_mmap_file(file))
 		return -ENODEV;
 
 	vma_set_file(vma, file);

fs/binfmt_elf.c

@@ -646,7 +646,7 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 	if (!elf_check_arch(interp_elf_ex) ||
 	    elf_check_fdpic(interp_elf_ex))
 		goto out;
-	if (!interpreter->f_op->mmap)
+	if (!can_mmap_file(interpreter))
 		goto out;
 
 	total_size = total_mapping_size(interp_elf_phdata,
@@ -848,7 +848,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 		goto out;
 	if (elf_check_fdpic(elf_ex))
 		goto out;
-	if (!bprm->file->f_op->mmap)
+	if (!can_mmap_file(bprm->file))
 		goto out;
 
 	elf_phdata = load_elf_phdrs(elf_ex, bprm->file);

fs/binfmt_elf_fdpic.c

@@ -109,7 +109,7 @@ static int is_elf(struct elfhdr *hdr, struct file *file)
 		return 0;
 	if (!elf_check_arch(hdr))
 		return 0;
-	if (!file->f_op->mmap)
+	if (!can_mmap_file(file))
 		return 0;
 	return 1;
 }

fs/coda/file.c

@@ -160,7 +160,7 @@ coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
 	size_t count;
 	int ret;
 
-	if (!host_file->f_op->mmap)
+	if (!can_mmap_file(host_file))
 		return -ENODEV;
 
 	if (WARN_ON(coda_file != vma->vm_file))

fs/ecryptfs/file.c

@@ -193,7 +193,7 @@ static int ecryptfs_mmap(struct file *file, struct vm_area_struct *vma)
 	 * natively.  If FILESYSTEM_MAX_STACK_DEPTH > 2 or ecryptfs
 	 * allows recursive mounting, this will need to be extended.
 	 */
-	if (!lower_file->f_op->mmap)
+	if (!can_mmap_file(lower_file))
 		return -ENODEV;
 	return generic_file_mmap(file, vma);
 }

include/linux/fs.h

@@ -2260,7 +2260,7 @@ struct inode_operations {
 } ____cacheline_aligned;
 
 /* Did the driver provide valid mmap hook configuration? */
-static inline bool file_has_valid_mmap_hooks(struct file *file)
+static inline bool can_mmap_file(struct file *file)
 {
 	bool has_mmap = file->f_op->mmap;
 	bool has_mmap_prepare = file->f_op->mmap_prepare;

mm/mmap.c

@@ -475,7 +475,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
 				vm_flags &= ~VM_MAYEXEC;
 			}
 
-			if (!file_has_valid_mmap_hooks(file))
+			if (!can_mmap_file(file))
 				return -ENODEV;
 			if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
 				return -EINVAL;

mm/nommu.c

@@ -719,7 +719,7 @@ static int validate_mmap_request(struct file *file,
 
 	if (file) {
 		/* files must support mmap */
-		if (!file_has_valid_mmap_hooks(file))
+		if (!can_mmap_file(file))
 			return -ENODEV;
 
 		/* work out if what we've got could possibly be shared

tools/testing/vma/vma_internal.h

@@ -1464,7 +1464,7 @@ static int compat_vma_mmap_prepare(struct file *file,
 }
 
 /* Did the driver provide valid mmap hook configuration? */
-static inline bool file_has_valid_mmap_hooks(struct file *file)
+static inline bool can_mmap_file(struct file *file)
 {
 	bool has_mmap = file->f_op->mmap;
 	bool has_mmap_prepare = file->f_op->mmap_prepare;