CVE-2021-47366

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.