From e3cf1cc9ed9230560e61306e13c88eccb5189c1b Mon Sep 17 00:00:00 2001 From: Theodore Ts'o Date: Mon, 7 May 2018 11:37:58 -0400 Subject: [PATCH] loop: add recursion validation to LOOP_CHANGE_FD 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 Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- drivers/block/loop.c | 68 +++++++++++++++++++++++++++++----------------------- 1 file changed, 38 insertions(+), 30 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index ff1c4d7..29c8471 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -640,6 +640,36 @@ static void loop_reread_partitions(struct loop_device *lo, __func__, lo->lo_number, lo->lo_file_name, rc); } +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 @@ -669,14 +699,15 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, 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; @@ -697,13 +728,6 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, 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, @@ -861,7 +885,7 @@ static int loop_prepare_queue(struct loop_device *lo) 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; @@ -881,29 +905,13 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, 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_iter) lo_flags |= LO_FLAGS_READ_ONLY; -- 2.7.4