From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: INFO: task hung in blk_freeze_queue To: Dmitry Vyukov , syzbot , Jens Axboe , Jan Kara Cc: linux-block@vger.kernel.org, LKML , syzkaller-bugs@googlegroups.com References: <001a113f64ee97b27105649a7cb2@google.com> From: Tetsuo Handa Message-ID: <69fc11b3-9d6a-5afb-3521-abd007ac9ad0@I-love.SAKURA.ne.jp> Date: Sat, 5 May 2018 13:26:38 +0900 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 List-ID: A patch for this specific report is ready. I don't know whether other "dup" reports will be solved by this patch. Thus, I "undup" this report. #syz undup >>From eed54c6ae475860a9c63b37b58f34735e792eef7 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa 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. Signed-off-by: Tetsuo Handa Reported-by: syzbot Cc: Jens Axboe --- 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