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Filename Latest commit message Latest commit date
Dongli Zhang f7c8a4120e loop: access lo_backing_file only when the loop device is Lo_bound
Commit 758a58d0bc ("loop: set GENHD_FL_NO_PART_SCAN after
blkdev_reread_part()") separates "lo->lo_backing_file = NULL" and
"lo->lo_state = Lo_unbound" into different critical regions protected by
loop_ctl_mutex.

However, there is below race that the NULL lo->lo_backing_file would be
accessed when the backend of a loop is another loop device, e.g., loop0's
backend is a file, while loop1's backend is loop0.

loop0's backend is file            loop1's backend is loop0

__loop_clr_fd()
  mutex_lock(&loop_ctl_mutex);
  lo->lo_backing_file = NULL; --> set to NULL
  mutex_unlock(&loop_ctl_mutex);
                                   loop_set_fd()
                                     mutex_lock_killable(&loop_ctl_mutex);
                                     loop_validate_file()
                                       f = l->lo_backing_file; --> NULL
                                         access if loop0 is not Lo_unbound
  mutex_lock(&loop_ctl_mutex);
  lo->lo_state = Lo_unbound;
  mutex_unlock(&loop_ctl_mutex);

lo->lo_backing_file should be accessed only when the loop device is
Lo_bound.

In fact, the problem has been introduced already in commit 7ccd0791d9
("loop: Push loop_ctl_mutex down into loop_clr_fd()") after which
loop_validate_file() could see devices in Lo_rundown state with which it
did not count. It was harmless at that point but still.

Fixes: 7ccd0791d9 ("loop: Push loop_ctl_mutex down into loop_clr_fd()")
Reported-by: syzbot+9bdc1adc1c55e7fe765b@syzkaller.appspotmail.com
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-03-18 08:20:53 -06:00
arch Kbuild updates for v5.1 (2nd) 2019-03-17 13:25:26 -07:00
block blk-mq: use blk_mq_sched_mark_restart_hctx to set RESTART 2019-03-18 08:14:51 -06:00
certs
crypto
Documentation Kbuild updates for v5.1 (2nd) 2019-03-17 13:25:26 -07:00
drivers loop: access lo_backing_file only when the loop device is Lo_bound 2019-03-18 08:20:53 -06:00
fs Pull request for inlusion in 5.1 2019-03-17 09:10:56 -07:00
include Kbuild updates for v5.1 (2nd) 2019-03-17 13:25:26 -07:00
init
ipc
kernel pidfd patches for v5.1-rc1 2019-03-16 13:47:14 -07:00
lib Kbuild updates for v5.1 (2nd) 2019-03-17 13:25:26 -07:00
LICENSES
mm
net Pull request for inlusion in 5.1 2019-03-17 09:10:56 -07:00
samples
scripts kconfig: remove stale lxdialog/.gitignore 2019-03-17 15:47:02 +09:00
security
sound
tools pidfd patches for v5.1-rc1 2019-03-16 13:47:14 -07:00
usr
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
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MAINTAINERS
Makefile Linux 5.1-rc1 2019-03-17 14:22:26 -07:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.