Re: [PATCH v3] fuse: In fuse_flush only wait if someone wants the return code

Miklos Szeredi
2022-12-08T14:27:35Z

[-- Attachment #1: Type: text/plain, Size: 477 bytes --]

On Mon, 28 Nov 2022 at 16:01, Tycho Andersen <tycho@tycho.pizza> wrote:
>
> Hi Milkos,
>
> On Mon, Nov 14, 2022 at 09:02:09AM -0700, Tycho Andersen wrote:
> > v3: use schedule_work() to avoid other sleeps in inode_write_now() and
> > fuse_sync_writes(). Fix a UAF of the stack-based inarg.
>
> Thoughts on this version?

Skipping attr invalidation on success is wrong. And there's still too
much duplication, IMO.

How about the attached (untested) patch?

Thanks,
Miklos

[-- Attachment #2: fuse-flush-async-if-exiting.patch --]
[-- Type: text/x-patch, Size: 3374 bytes --]

---
fs/fuse/file.c | 89 ++++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 63 insertions(+), 26 deletions(-)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -18,6 +18,7 @@
#include <linux/falloc.h>
#include <linux/uio.h>
#include <linux/fs.h>
+#include <linux/file.h>

static int fuse_send_open(struct fuse_mount *fm, u64 nodeid,
unsigned int open_flags, int opcode,
@@ -477,48 +478,36 @@ static void fuse_sync_writes(struct inod
fuse_release_nowrite(inode);
}

-static int fuse_flush(struct file *file, fl_owner_t id)
-{
- struct inode *inode = file_inode(file);
- struct fuse_mount *fm = get_fuse_mount(inode);
- struct fuse_file *ff = file->private_data;
+struct fuse_flush_args {
+ struct fuse_args args;
struct fuse_flush_in inarg;
- FUSE_ARGS(args);
- int err;
-
- if (fuse_is_bad(inode))
- return -EIO;
+ struct work_struct work;
+ struct file *file;
+};

- if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
- return 0;
+static int fuse_do_flush(struct fuse_flush_args *fa)
+{
+ int err;
+ struct inode *inode = file_inode(fa->file);
+ struct fuse_mount *fm = get_fuse_mount(inode);

err = write_inode_now(inode, 1);
if (err)
- return err;
+ goto out;

inode_lock(inode);
fuse_sync_writes(inode);
inode_unlock(inode);

- err = filemap_check_errors(file->f_mapping);
+ err = filemap_check_errors(fa->file->f_mapping);
if (err)
- return err;
+ goto out;

err = 0;
if (fm->fc->no_flush)
goto inval_attr_out;

- memset(&inarg, 0, sizeof(inarg));
- inarg.fh = ff->fh;
- inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
- args.opcode = FUSE_FLUSH;
- args.nodeid = get_node_id(inode);
- args.in_numargs = 1;
- args.in_args[0].size = sizeof(inarg);
- args.in_args[0].value = &inarg;
- args.force = true;
-
- err = fuse_simple_request(fm, &args);
+ err = fuse_simple_request(fm, &fa->args);
if (err == -ENOSYS) {
fm->fc->no_flush = 1;
err = 0;
@@ -531,9 +520,57 @@ static int fuse_flush(struct file *file,
*/
if (!err && fm->fc->writeback_cache)
fuse_invalidate_attr_mask(inode, STATX_BLOCKS);
+
+out:
+ fput(fa->file);
+ kfree(fa);
return err;
}

+static void fuse_flush_async(struct work_struct *work)
+{
+ struct fuse_flush_args *fa = container_of(work, typeof(*fa), work);
+
+ fuse_do_flush(fa);
+}
+
+static int fuse_flush(struct file *file, fl_owner_t id)
+{
+ struct fuse_flush_args *fa;
+ struct inode *inode = file_inode(file);
+ struct fuse_mount *fm = get_fuse_mount(inode);
+ struct fuse_file *ff = file->private_data;
+
+ if (fuse_is_bad(inode))
+ return -EIO;
+
+ if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
+ return 0;
+
+ fa = kzalloc(sizeof(*fa), GFP_KERNEL);
+ if (!fa)
+ return -ENOMEM;
+
+ fa->inarg.fh = ff->fh;
+ fa->inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
+ fa->args.opcode = FUSE_FLUSH;
+ fa->args.nodeid = get_node_id(inode);
+ fa->args.in_numargs = 1;
+ fa->args.in_args[0].size = sizeof(fa->inarg);
+ fa->args.in_args[0].value = &fa->inarg;
+ fa->args.force = true;
+ fa->file = get_file(file);
+
+ /* Don't wait if the task is exiting */
+ if (current->flags & PF_EXITING) {
+ INIT_WORK(&fa->work, fuse_flush_async);
+ schedule_work(&fa->work);
+ return 0;
+ }
+
+ return fuse_do_flush(fa);
+}
+
int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
int datasync, int opcode)
{