3.18-stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o tytso@mit.edu
commit d2ac838e4cd7e5e9891ecc094d626734b0245c99 upstream.
Refactor the validation code used in LOOP_SET_FD so it is also used in LOOP_CHANGE_FD. Otherwise it is possible to construct a set of loop devices that all refer to each other. This can lead to a infinite loop in starting with "while (is_loop_device(f)) .." in loop_set_fd().
Fix this by refactoring out the validation code and using it for LOOP_CHANGE_FD as well as LOOP_SET_FD.
Reported-by: syzbot+4349872271ece473a7c91190b68b4bac7c5dbc87@syzkaller.appspotmail.com Reported-by: syzbot+40bd32c4d9a3cc12a339@syzkaller.appspotmail.com Reported-by: syzbot+769c54e66f994b041be7@syzkaller.appspotmail.com Reported-by: syzbot+0a89a9ce473936c57065@syzkaller.appspotmail.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/block/loop.c | 68 ++++++++++++++++++++++++++++----------------------- 1 file changed, 38 insertions(+), 30 deletions(-)
--- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -628,6 +628,36 @@ out: }
+static inline int is_loop_device(struct file *file) +{ + struct inode *i = file->f_mapping->host; + + return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR; +} + +static int loop_validate_file(struct file *file, struct block_device *bdev) +{ + struct inode *inode = file->f_mapping->host; + struct file *f = file; + + /* Avoid recursion */ + while (is_loop_device(f)) { + struct loop_device *l; + + if (f->f_mapping->host->i_bdev == bdev) + return -EBADF; + + l = f->f_mapping->host->i_bdev->bd_disk->private_data; + if (l->lo_state == Lo_unbound) { + return -EINVAL; + } + f = l->lo_backing_file; + } + if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode)) + return -EINVAL; + return 0; +} + /* * 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 @@ -657,14 +687,15 @@ static int loop_change_fd(struct loop_de if (!file) goto out;
+ error = loop_validate_file(file, bdev); + if (error) + goto out_putf; + inode = file->f_mapping->host; old_file = lo->lo_backing_file;
error = -EINVAL;
- if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode)) - goto out_putf; - /* size of the new backing store needs to be the same */ if (get_loop_size(lo, file) != get_loop_size(lo, old_file)) goto out_putf; @@ -685,13 +716,6 @@ static int loop_change_fd(struct loop_de return error; }
-static inline int is_loop_device(struct file *file) -{ - struct inode *i = file->f_mapping->host; - - return i && S_ISBLK(i->i_mode) && MAJOR(i->i_rdev) == LOOP_MAJOR; -} - /* loop sysfs attributes */
static ssize_t loop_attr_show(struct device *dev, char *page, @@ -823,7 +847,7 @@ static void loop_config_discard(struct l static int loop_set_fd(struct loop_device *lo, fmode_t mode, struct block_device *bdev, unsigned int arg) { - struct file *file, *f; + struct file *file; struct inode *inode; struct address_space *mapping; unsigned lo_blocksize; @@ -843,29 +867,13 @@ static int loop_set_fd(struct loop_devic if (lo->lo_state != Lo_unbound) goto out_putf;
- /* Avoid recursion */ - f = file; - while (is_loop_device(f)) { - struct loop_device *l; - - if (f->f_mapping->host->i_bdev == bdev) - goto out_putf; - - l = f->f_mapping->host->i_bdev->bd_disk->private_data; - if (l->lo_state == Lo_unbound) { - error = -EINVAL; - goto out_putf; - } - f = l->lo_backing_file; - } + error = loop_validate_file(file, bdev); + if (error) + goto out_putf;
mapping = file->f_mapping; inode = mapping->host;
- error = -EINVAL; - if (!S_ISREG(inode->i_mode) && !S_ISBLK(inode->i_mode)) - goto out_putf; - if (!(file->f_mode & FMODE_WRITE) || !(mode & FMODE_WRITE) || !file->f_op->write) lo_flags |= LO_FLAGS_READ_ONLY;