[PATCH 3.16 42/47] coda: pass the host file in vma->vm_file on mmap

Ben Hutchings
2019-10-25T18:07:03Z

From: Jan Harkes <jaharkes@cs.cmu.edu>

commit 7fa0a1da3dadfd9216df7745a1331fdaa0940d1c upstream.

Patch series "Coda updates".

The following patch series is a collection of various fixes for Coda,
most of which were collected from linux-fsdevel or linux-kernel but
which have as yet not found their way upstream.

This patch (of 22):

Various file systems expect that vma->vm_file points at their own file
handle, several use file_inode(vma->vm_file) to get at their inode or
use vma->vm_file->private_data. However the way Coda wrapped mmap on a
host file broke this assumption, vm_file was still pointing at the Coda
file and the host file systems would scribble over Coda's inode and
private file data.

This patch fixes the incorrect expectation and wraps vm_ops->open and
vm_ops->close to allow Coda to track when the vm_area_struct is
destroyed so we still release the reference on the Coda file handle at
the right time.

Link: http://lkml.kernel.org/r/0e850c6e59c0b147dc2dcd51a3af004c948c3697.1558117389.git.jaharkes@cs.cmu.edu
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Mikko Rapeli <mikko.rapeli@iki.fi>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Zhouyang Jia <jiazhouyang09@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: Keep calling file_operations::mmap directly]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/coda/file.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 68 insertions(+), 2 deletions(-)

--- a/fs/coda/file.c
+++ b/fs/coda/file.c
@@ -26,6 +26,13 @@
#include "coda_linux.h"
#include "coda_int.h"

+struct coda_vm_ops {
+ atomic_t refcnt;
+ struct file *coda_file;
+ const struct vm_operations_struct *host_vm_ops;
+ struct vm_operations_struct vm_ops;
+};
+
static ssize_t
coda_file_read(struct file *coda_file, char __user *buf, size_t count, loff_t *ppos)
{
@@ -93,6 +100,34 @@ coda_file_write(struct file *coda_file,
return ret;
}

+static void
+coda_vm_open(struct vm_area_struct *vma)
+{
+ struct coda_vm_ops *cvm_ops =
+ container_of(vma->vm_ops, struct coda_vm_ops, vm_ops);
+
+ atomic_inc(&cvm_ops->refcnt);
+
+ if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->open)
+ cvm_ops->host_vm_ops->open(vma);
+}
+
+static void
+coda_vm_close(struct vm_area_struct *vma)
+{
+ struct coda_vm_ops *cvm_ops =
+ container_of(vma->vm_ops, struct coda_vm_ops, vm_ops);
+
+ if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->close)
+ cvm_ops->host_vm_ops->close(vma);
+
+ if (atomic_dec_and_test(&cvm_ops->refcnt)) {
+ vma->vm_ops = cvm_ops->host_vm_ops;
+ fput(cvm_ops->coda_file);
+ kfree(cvm_ops);
+ }
+}
+
static int
coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
{
@@ -100,6 +135,8 @@ coda_file_mmap(struct file *coda_file, s
struct coda_inode_info *cii;
struct file *host_file;
struct inode *coda_inode, *host_inode;
+ struct coda_vm_ops *cvm_ops;
+ int ret;

cfi = CODA_FTOC(coda_file);
BUG_ON(!cfi || cfi->cfi_magic != CODA_MAGIC);
@@ -108,6 +145,13 @@ coda_file_mmap(struct file *coda_file, s
if (!host_file->f_op->mmap)
return -ENODEV;

+ if (WARN_ON(coda_file != vma->vm_file))
+ return -EIO;
+
+ cvm_ops = kmalloc(sizeof(struct coda_vm_ops), GFP_KERNEL);
+ if (!cvm_ops)
+ return -ENOMEM;
+
coda_inode = file_inode(coda_file);
host_inode = file_inode(host_file);

@@ -121,6 +165,7 @@ coda_file_mmap(struct file *coda_file, s
* the container file on us! */
else if (coda_inode->i_mapping != host_inode->i_mapping) {
spin_unlock(&cii->c_lock);
+ kfree(cvm_ops);
return -EBUSY;
}

@@ -129,7 +174,29 @@ coda_file_mmap(struct file *coda_file, s
cfi->cfi_mapcount++;
spin_unlock(&cii->c_lock);

- return host_file->f_op->mmap(host_file, vma);
+ vma->vm_file = get_file(host_file);
+ ret = host_file->f_op->mmap(host_file, vma);
+
+ if (ret) {
+ /* if ->mmap fails, our caller will put coda_file so we
+ * should drop the reference to the host_file that we got.
+ */
+ fput(host_file);
+ kfree(cvm_ops);
+ } else {
+ /* here we add redirects for the open/close vm_operations */
+ cvm_ops->host_vm_ops = vma->vm_ops;
+ if (vma->vm_ops)
+ cvm_ops->vm_ops = *vma->vm_ops;
+
+ cvm_ops->vm_ops.open = coda_vm_open;
+ cvm_ops->vm_ops.close = coda_vm_close;
+ cvm_ops->coda_file = coda_file;
+ atomic_set(&cvm_ops->refcnt, 1);
+
+ vma->vm_ops = &cvm_ops->vm_ops;
+ }
+ return ret;
}

int coda_open(struct inode *coda_inode, struct file *coda_file)
@@ -239,4 +306,3 @@ const struct file_operations coda_file_o
.fsync = coda_fsync,
.splice_read = coda_file_splice_read,
};
-