Vulnerabilities > CVE-2021-47587 - Improper Locking vulnerability in Linux Kernel
Summary
In the Linux kernel, the following vulnerability has been resolved: net: systemport: Add global locking for descriptor lifecycle The descriptor list is a shared resource across all of the transmit queues, and the locking mechanism used today only protects concurrency across a given transmit queue between the transmit and reclaiming. This creates an opportunity for the SYSTEMPORT hardware to work on corrupted descriptors if we have multiple producers at once which is the case when using multiple transmit queues. This was particularly noticeable when using multiple flows/transmit queues and it showed up in interesting ways in that UDP packets would get a correct UDP header checksum being calculated over an incorrect packet length. Similarly TCP packets would get an equally correct checksum computed by the hardware over an incorrect packet length. The SYSTEMPORT hardware maintains an internal descriptor list that it re-arranges when the driver produces a new descriptor anytime it writes to the WRITE_PORT_{HI,LO} registers, there is however some delay in the hardware to re-organize its descriptors and it is possible that concurrent TX queues eventually break this internal allocation scheme to the point where the length/status part of the descriptor gets used for an incorrect data buffer. The fix is to impose a global serialization for all TX queues in the short section where we are writing to the WRITE_PORT_{HI,LO} registers which solves the corruption even with multiple concurrent TX queues being used.
Vulnerable Configurations
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Leveraging Race Conditions This attack targets a race condition occurring when multiple processes access and manipulate the same resource concurrently and the outcome of the execution depends on the particular order in which the access takes place. The attacker can leverage a race condition by "running the race", modifying the resource and modifying the normal execution flow. For instance a race condition can occur while accessing a file, the attacker can trick the system by replacing the original file with his version and cause the system to read the malicious file.
- Leveraging Race Conditions via Symbolic Links This attack leverages the use of symbolic links (Symlinks) in order to write to sensitive files. An attacker can create a Symlink link to a target file not otherwise accessible to her. When the privileged program tries to create a temporary file with the same name as the Symlink link, it will actually write to the target file pointed to by the attackers' Symlink link. If the attacker can insert malicious content in the temporary file she will be writing to the sensitive file by using the Symlink. The race occurs because the system checks if the temporary file exists, then creates the file. The attacker would typically create the Symlink during the interval between the check and the creation of the temporary file.
References
- https://git.kernel.org/stable/c/8ed2f5d08d6e59f8c78b2869bfb95d0be32c094c
- https://git.kernel.org/stable/c/de57f62f76450b934de8203711bdc4f7953c3421
- https://git.kernel.org/stable/c/f3fde37d3f0d429f0fcce214cb52588a9e21260e
- https://git.kernel.org/stable/c/595a684fa6f23b21958379a18cfa83862c73c2e1
- https://git.kernel.org/stable/c/c675256a7f131f5ba3f331efb715e8f31ea0e392
- https://git.kernel.org/stable/c/6e1011cd183faae8daff275c72444edcdfe0d473
- https://git.kernel.org/stable/c/eb4687c7442942e115420a30185f8d83faf37696
- https://git.kernel.org/stable/c/8b8e6e782456f1ce02a7ae914bbd5b1053f0b034