Oh, your message did not arrive at news.gmane.org and I didn't notice that you already wrote this patch. But please update yours or review mine shown below. > @@ -673,14 +703,13 @@ 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; error == 0 upon "goto out_putf" is wrong. >From eed54c6ae475860a9c63b37b58f34735e792eef7 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Date: Sat, 5 May 2018 12:59:12 +0900 Subject: [PATCH] block/loop: Add recursion check for LOOP_CHANGE_FD request. syzbot is reporting hung tasks at blk_freeze_queue() [1]. This is due to ioctl(loop_fd, LOOP_CHANGE_FD, loop_fd) request which should be rejected. Fix this by adding same recursion check which is used by LOOP_SET_FD request. [1] https://syzkaller.appspot.com/bug?id=078805a692853552e08154b1bcd2bc2c729eda88 Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Reported-by: syzbot <syzbot+2ab52b8d94df5e2eaa01@xxxxxxxxxxxxxxxxxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> --- drivers/block/loop.c | 59 ++++++++++++++++++++++++++++++++-------------------- 1 file changed, 37 insertions(+), 22 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 5d4e316..cee3c01 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -644,6 +644,34 @@ 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 check_loop_recursion(struct file *f, struct block_device *bdev) +{ + /* + * FIXME: Traversing on other loop devices without corresponding + * lo_ctl_mutex is not safe. l->lo_state can become Lo_rundown and + * l->lo_backing_file can become NULL when raced with LOOP_CLR_FD. + */ + while (is_loop_device(f)) { + struct loop_device *l; + + if (f->f_mapping->host->i_bdev == bdev) + return -EBUSY; + + l = f->f_mapping->host->i_bdev->bd_disk->private_data; + if (l->lo_state == Lo_unbound) + return -EINVAL; + f = l->lo_backing_file; + } + 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 @@ -673,6 +701,11 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev, if (!file) goto out; + /* Avoid recursion */ + error = check_loop_recursion(file, bdev); + if (error) + goto out_putf; + inode = file->f_mapping->host; old_file = lo->lo_backing_file; @@ -706,13 +739,6 @@ 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, @@ -877,7 +903,7 @@ 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; int lo_flags = 0; @@ -897,20 +923,9 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, 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 = check_loop_recursion(file, bdev); + if (error) + goto out_putf; mapping = file->f_mapping; inode = mapping->host; -- 1.8.3.1
