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Filipe Manana 8155dbe015 Btrfs: fix negative subv_writers counter and data space leak after buffered write 
commit a0e248bb50 upstream.

When doing a buffered write it's possible to leave the subv_writers
counter of the root, used for synchronization between buffered nocow
writers and snapshotting. This happens in an exceptional case like the
following:

1) We fail to allocate data space for the write, since there's not
   enough available data space nor enough unallocated space for allocating
   a new data block group;

2) Because of that failure, we try to go to NOCOW mode, which succeeds
   and therefore we set the local variable 'only_release_metadata' to true
   and set the root's sub_writers counter to 1 through the call to
   btrfs_start_write_no_snapshotting() made by check_can_nocow();

3) The call to btrfs_copy_from_user() returns zero, which is very unlikely
   to happen but not impossible;

4) No pages are copied because btrfs_copy_from_user() returned zero;

5) We call btrfs_end_write_no_snapshotting() which decrements the root's
   subv_writers counter to 0;

6) We don't set 'only_release_metadata' back to 'false' because we do
   it only if 'copied', the value returned by btrfs_copy_from_user(), is
   greater than zero;

7) On the next iteration of the while loop, which processes the same
   page range, we are now able to allocate data space for the write (we
   got enough data space released in the meanwhile);

8) After this if we fail at btrfs_delalloc_reserve_metadata(), because
   now there isn't enough free metadata space, or in some other place
   further below (prepare_pages(), lock_and_cleanup_extent_if_need(),
   btrfs_dirty_pages()), we break out of the while loop with
   'only_release_metadata' having a value of 'true';

9) Because 'only_release_metadata' is 'true' we end up decrementing the
   root's subv_writers counter to -1 (through a call to
   btrfs_end_write_no_snapshotting()), and we also end up not releasing the
   data space previously reserved through btrfs_check_data_free_space().
   As a consequence the mechanism for synchronizing NOCOW buffered writes
   with snapshotting gets broken.

Fix this by always setting 'only_release_metadata' to false at the start
of each iteration.

Fixes: 8257b2dc3c ("Btrfs: introduce btrfs_{start, end}_nocow_write() for each subvolume")
Fixes: 7ee9e4405f ("Btrfs: check if we can nocow if we don't have data space")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-12-17 20:34:47 +01:00
arch ARM: dts: pandora-common: define wl1251 as child node of mmc3 2019-12-17 20:34:36 +01:00
block block: call rq_qos_exit() after queue is frozen 2019-12-01 09:17:06 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: user - fix memory leak in crypto_report 2019-12-13 08:52:48 +01:00
Documentation USB: documentation: flags on usb-storage versus UAS 2019-12-17 20:34:30 +01:00
drivers phy: renesas: rcar-gen3-usb2: Fix sysfs interface of "role" 2019-12-17 20:34:45 +01:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Btrfs: fix negative subv_writers counter and data space leak after buffered write 2019-12-17 20:34:47 +01:00
include appletalk: Fix potential NULL pointer dereference in unregister_snap_client 2019-12-13 08:52:59 +01:00
init fork: fix some -Wmissing-prototypes warnings 2019-12-05 09:21:04 +01:00
ipc ipc/mqueue.c: only perform resource calculation if user valid 2019-08-06 19:06:52 +02:00
kernel sched/fair: Scale bandwidth quota and period without losing quota/period ratio precision 2019-12-13 08:52:35 +01:00
lib lib/genalloc.c: include vmalloc.h 2019-12-05 09:21:05 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/vmstat.c: fix NUMA statistics updates 2019-12-13 08:51:27 +01:00
net appletalk: Set error code if register_snap_client failed 2019-12-13 08:52:59 +01:00
samples vfio-mdev/samples: Use u8 instead of char for handle functions 2019-12-05 09:20:28 +01:00
scripts modpost: skip ELF local symbols during section mismatch check 2019-12-13 08:52:20 +01:00
security apparmor: delete the dentry in aafs_remove() to avoid a leak 2019-12-05 09:21:19 +01:00
sound ASoC: rsnd: fixup MIX kctrl registration 2019-12-13 08:52:57 +01:00
tools perf script: Fix invalid LBR/binary mismatch error 2019-12-13 08:52:55 +01:00
usr kbuild: clean compressed initramfs image 2019-10-07 18:57:16 +02:00
virt KVM: arm/arm64: vgic: Don't rely on the wrong pending table 2019-12-13 08:52:45 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS USB: rio500: Remove Rio 500 kernel driver 2019-10-17 13:44:47 -07:00
Makefile Linux 4.19.89 2019-12-13 08:52:59 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.