afs: Fix directory entry size calculation

The number of dirent records used by an AFS directory entry should be
calculated using the assumption that there is a 16-byte name field in the
first block, rather than a 20-byte name field (which is actually the case).
This miscalculation is historic and effectively standard, so we have to use
it.

The calculation we need to use is:

1 + (((strlen(name) + 1) + 15) >> 5)

where we are adding one to the strlen() result to account for the NUL
termination.

Fix this by the following means:

(1) Create an inline function to do the calculation for a given name
length.

(2) Use the function to calculate the number of records used for a dirent
in afs_dir_iterate_block().

Use this to move the over-end check out of the loop since it only
needs to be done once.

Further use this to only go through the loop for the 2nd+ records
composing an entry. The only test there now is for if the record is
allocated - and we already checked the first block at the top of the
outer loop.

(3) Add a max name length check in afs_dir_iterate_block().

(4) Make afs_edit_dir_add() and afs_edit_dir_remove() use the function
from (1) to calculate the number of blocks rather than doing it
incorrectly themselves.

Fixes: 63a4681ff39c ("afs: Locally edit directory data for mkdir/create/unlink/...")
Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>

afs: Work around strnlen() oops with CONFIG_FORTIFIED_SOURCE=y

AFS has a structured layout in its directory contents (AFS dirs are
downloaded as files and parsed locally by the client for lookup/readdir).
The slots in the directory are defined by union afs_xdr_dirent. This,
however, only directly allows a name of a length that will fit into that
union. To support a longer name, the next 1-8 contiguous entries are
annexed to the first one and the name flows across these.

afs_dir_iterate_block() uses strnlen(), limited to the space to the end of
the page, to find out how long the name is. This worked fine until
6a39e62abbaf. With that commit, the compiler determines the size of the
array and asserts that the string fits inside that array. This is a
problem for AFS because we *expect* it to overflow one or more arrays.

A similar problem also occurs in afs_dir_scan_block() when a directory file
is being locally edited to avoid the need to redownload it. There strlen()
was being used safely because each page has the last byte set to 0 when the
file is downloaded and validated (in afs_dir_check_page()).

Fix this by changing the afs_xdr_dirent union name field to an
indeterminate-length array and dropping the overflow field.

(Note that whilst looking at this, I realised that the calculation of the
number of slots a dirent used is non-standard and not quite right, but I'll
address that in a separate patch.)

The issue can be triggered by something like:

touch /afs/example.com/thisisaveryveryverylongname

and it generates a report that looks like:

detected buffer overflow in strnlen
------------[ cut here ]------------
kernel BUG at lib/string.c:1149!
...
RIP: 0010:fortify_panic+0xf/0x11
...
Call Trace:
afs_dir_iterate_block+0x12b/0x35b
afs_dir_iterate+0x14e/0x1ce
afs_do_lookup+0x131/0x417
afs_lookup+0x24f/0x344
lookup_open.isra.0+0x1bb/0x27d
open_last_lookups+0x166/0x237
path_openat+0xe0/0x159
do_filp_open+0x48/0xa4
? kmem_cache_alloc+0xf5/0x16e
? __clear_close_on_exec+0x13/0x22
? _raw_spin_unlock+0xa/0xb
do_sys_openat2+0x72/0xde
do_sys_open+0x3b/0x58
do_syscall_64+0x2d/0x3a
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 6a39e62abbaf ("lib: string.h: detect intra-object overflow in fortified string functions")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marc Dionne <marc.dionne@auristor.com>
cc: Daniel Axtens <dja@axtens.net>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public licence as published by
the free software foundation either version 2 of the licence or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 114 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190520170857.552531963@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

afs: Adjust the directory XDR structures

Adjust the AFS directory XDR structures in a number of superficial ways:

(1) Rename them to all begin afs_xdr_.

(2) Use u8 instead of uint8_t.

(3) Mark the structures as __packed so they don't get rearranged by the
compiler.

(4) Rename the hdr member of afs_xdr_dir_block to meta.

(5) Rename the pagehdr member of afs_xdr_dir_block to hdr.

Signed-off-by: David Howells <dhowells@redhat.com>

afs: Split the directory content defs into a header

Split the directory content definitions into a header file so that they can
be used by multiple .c files.

Signed-off-by: David Howells <dhowells@redhat.com>

afs: Rearrange status mapping

Rearrange the AFSFetchStatus to inode attribute mapping code in a number of
ways:

(1) Use an XDR structure rather than a series of incremented pointer
accesses when decoding an AFSFetchStatus object. This allows
out-of-order decode.

(2) Don't store the if_version value but rather just check it and abort if
it's not something we can handle.

(3) Store the owner and group in the status record as raw values rather
than converting them to kuid/kgid. Do that when they're mapped into
i_uid/i_gid.

(4) Validate the type and abort code up front and abort if they're wrong.

(5) Split the inode attribute setting out into its own function from the
XDR decode of an AFSFetchStatus object. This allows it to be called
from elsewhere too.

(6) Differentiate changes to data from changes to metadata.

(7) Use the split-out attribute mapping function from afs_iget().

Signed-off-by: David Howells <dhowells@redhat.com>