Subject: CVE-2021-47366: afs: Fix corruption in reads at fpos 2G-4G from an OpenAFS server

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

afs: Fix corruption in reads at fpos 2G-4G from an OpenAFS server

AFS-3 has two data fetch RPC variants, FS.FetchData and FS.FetchData64, and
Linux's afs client switches between them when talking to a non-YFS server
if the read size, the file position or the sum of the two have the upper 32
bits set of the 64-bit value.

This is a problem, however, since the file position and length fields of
FS.FetchData are *signed* 32-bit values.

Fix this by capturing the capability bits obtained from the fileserver when
it's sent an FS.GetCapabilities RPC, rather than just discarding them, and
then picking out the VICED_CAPABILITY_64BITFILES flag.  This can then be
used to decide whether to use FS.FetchData or FS.FetchData64 - and also
FS.StoreData or FS.StoreData64 - rather than using upper_32_bits() to
switch on the parameter values.

This capabilities flag could also be used to limit the maximum size of the
file, but all servers must be checked for that.

Note that the issue does not exist with FS.StoreData - that uses *unsigned*
32-bit values.  It's also not a problem with Auristor servers as its
YFS.FetchData64 op uses unsigned 64-bit values.

This can be tested by cloning a git repo through an OpenAFS client to an
OpenAFS server and then doing "git status" on it from a Linux afs
client[1].  Provided the clone has a pack file that's in the 2G-4G range,
the git status will show errors like:

	error: packfile .git/objects/pack/pack-5e813c51d12b6847bbc0fcd97c2bca66da50079c.pack does not match index
	error: packfile .git/objects/pack/pack-5e813c51d12b6847bbc0fcd97c2bca66da50079c.pack does not match index

This can be observed in the server's FileLog with something like the
following appearing:

Sun Aug 29 19:31:39 2021 SRXAFS_FetchData, Fid = 2303380852.491776.3263114, Host 192.168.11.201:7001, Id 1001
Sun Aug 29 19:31:39 2021 CheckRights: len=0, for host=192.168.11.201:7001
Sun Aug 29 19:31:39 2021 FetchData_RXStyle: Pos 18446744071815340032, Len 3154
Sun Aug 29 19:31:39 2021 FetchData_RXStyle: file size 2400758866
...
Sun Aug 29 19:31:40 2021 SRXAFS_FetchData returns 5

Note the file position of 18446744071815340032.  This is the requested file
position sign-extended.

The Linux kernel CVE team has assigned CVE-2021-47366 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 2.6.22 with commit b9b1f8d5930a and fixed in 5.14.9 with commit e66fc460d6dc
	Issue introduced in 2.6.22 with commit b9b1f8d5930a and fixed in 5.15 with commit b537a3c21775

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47366
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/afs/fs_probe.c
	fs/afs/fsclient.c
	fs/afs/internal.h
	fs/afs/protocol_afs.h
	fs/afs/protocol_yfs.h

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/e66fc460d6dcf85cf12288e133a081205aebcd97
	https://git.kernel.org/stable/c/b537a3c21775075395af475dcc6ef212fcf29db8