CVE-2021-47366 afs: Fix corruption in reads at fpos 2G-4G from an OpenAFS server
A signed integer overflow in the Linux kernel AFS client causes data corruption when reading files between 2GB and 4GB from OpenAFS servers.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47366?
CVE-2021-47366 is a high-severity vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-787
Which versions are affected by CVE-2021-47366?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47366?
Apply the vendor's patch.
Is CVE-2021-47366 being exploited?
There is no known exploitation of CVE-2021-47366 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47366, GHSA-27rv-f8p8-59gg, ROOT-OS-DEBIAN-11-CVE-2021-47366, UBUNTU-CVE-2021-47366.