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loop: Add sanity check for read/write_iter

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Some file systems do not support read_iter/write_iter, such as selinuxfs
in this issue.
So before calling them, first confirm that the interface is supported and
then call it.

It is releavant in that vfs_iter_read/write have the check, and removal
of their used caused szybot to be able to hit this issue.

Fixes: f2fed441c6 ("loop: stop using vfs_iter__{read,write} for buffered I/O")
Reported-by: syzbot+6af973a3b8dfd2faefdc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6af973a3b8dfd2faefdc
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250428143626.3318717-1-lizhi.xu@windriver.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Lizhi Xu 2025-04-28 22:36:26 +08:00 committed by Jens Axboe
parent 6d732e8d1e
commit f5c84eff63
1 changed files with 23 additions and 0 deletions
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23
drivers/block/loop.c
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@ -505,6 +505,17 @@ static void loop_assign_backing_file(struct loop_device *lo, struct file *file)
lo->lo_min_dio_size = loop_query_min_dio_size(lo); lo->lo_min_dio_size = loop_query_min_dio_size(lo);
} }
static int loop_check_backing_file(struct file *file)
{
if (!file->f_op->read_iter)
return -EINVAL;
if ((file->f_mode & FMODE_WRITE) && !file->f_op->write_iter)
return -EINVAL;
return 0;
}
/* /*
* loop_change_fd switched the backing store of a loopback device to * loop_change_fd switched the backing store of a loopback device to
* a new file. This is useful for operating system installers to free up * a new file. This is useful for operating system installers to free up
@ -526,6 +537,10 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
if (!file) if (!file)
return -EBADF; return -EBADF;
error = loop_check_backing_file(file);
if (error)
return error;
/* suppress uevents while reconfiguring the device */ /* suppress uevents while reconfiguring the device */
dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1); dev_set_uevent_suppress(disk_to_dev(lo->lo_disk), 1);
@ -963,6 +978,14 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
if (!file) if (!file)
return -EBADF; return -EBADF;
if ((mode & BLK_OPEN_WRITE) && !file->f_op->write_iter)
return -EINVAL;
error = loop_check_backing_file(file);
if (error)
return error;
is_loop = is_loop_device(file); is_loop = is_loop_device(file);
/* This is safe, since we have a reference from open(). */ /* This is safe, since we have a reference from open(). */