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Al Viro d76341d93d vfs: fix do_last() regression
commit 6404674acd upstream.

Brown paperbag time: fetching ->i_uid/->i_mode really should've been
done from nd->inode.  I even suggested that, but the reason for that has
slipped through the cracks and I went for dir->d_inode instead - made
for more "obvious" patch.

Analysis:

 - at the entry into do_last() and all the way to step_into(): dir (aka
   nd->path.dentry) is known not to have been freed; so's nd->inode and
   it's equal to dir->d_inode unless we are already doomed to -ECHILD.
   inode of the file to get opened is not known.

 - after step_into(): inode of the file to get opened is known; dir
   might be pointing to freed memory/be negative/etc.

 - at the call of may_create_in_sticky(): guaranteed to be out of RCU
   mode; inode of the file to get opened is known and pinned; dir might
   be garbage.

The last was the reason for the original patch.  Except that at the
do_last() entry we can be in RCU mode and it is possible that
nd->path.dentry->d_inode has already changed under us.

In that case we are going to fail with -ECHILD, but we need to be
careful; nd->inode is pointing to valid struct inode and it's the same
as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we
should use that.

Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com>
Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com
Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@kernel.org
Fixes: d0cb50185a ("do_last(): fetch directory ->i_mode and ->i_uid before it's too late")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2020-02-04 18:18:00 +00:00
arch Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
block block: allow partitions on host aware zone devices 2020-01-26 09:59:08 -07:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto crypto: pcrypt - Fix user-after-free on module unload 2020-02-01 09:33:00 +00:00
Documentation Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-01-25 14:19:32 -08:00
drivers power/supply: ingenic-battery: Don't change scale if there's only one 2020-02-01 09:33:00 +00:00
fs vfs: fix do_last() regression 2020-02-04 18:18:00 +00:00
include udp: segment looped gso packets correctly 2020-02-01 09:32:58 +00:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
ipc treewide: Use sizeof_field() macro 2019-12-09 10:36:44 -08:00
kernel Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
lib lib: Reduce user_access_begin() boundaries in strncpy_from_user() and strnlen_user() 2020-01-24 09:27:34 -08:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: memcg/slab: call flush_memcg_workqueue() only if memcg workqueue is valid 2020-01-13 18:19:02 -08:00
net rxrpc: Fix use-after-free in rxrpc_receive_data() 2020-02-01 09:32:59 +00:00
samples samples/seccomp: Zero out members based on seccomp_notif_sizes 2020-01-02 13:03:39 -08:00
scripts ARM fixes for 5.5: 2020-01-25 14:32:51 -08:00
security + Bug fixes 2020-01-04 19:28:30 -08:00
sound sound fixes for 5.5-rc7 2020-01-17 08:38:35 -08:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-01-19 12:03:53 -08:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt PPC KVM fix for 5.5 2019-12-22 13:18:15 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap MAINTAINERS: update my email address 2020-01-11 14:33:39 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS tipc: change maintainer email address 2020-01-25 10:18:02 +01:00
Makefile Linux 5.5.1 2020-02-01 09:33:01 +00:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.