CVE-2024-27058

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

tmpfs: fix race on handling dquot rbtree

A syzkaller reproducer found a race while attempting to remove dquot information from the rb tree.

Fetching the rb_tree root node must also be protected by the dqopt->dqio_sem, otherwise, giving the right timing, shmem_release_dquot() will trigger a warning because it couldnt find a node in the tree, when the real reason was the root node changing before the search starts:

Thread 1 Thread 2

• shmem_release_dquot() - shmem_{acquire,release}_dquot()

• fetch ROOT - Fetch ROOT

    			- acquire dqio_sem
  

• wait dqio_sem

    			- do something, triger a tree rebalance
    			- release dqio_sem
  

• acquire dqio_sem

• start searching for the node, but from the wrong location, missing the node, and triggering a warning.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/0a69b6b3a026543bc215ccc866d0aea5579e6ce2
• https://git.kernel.org/stable/c/617d55b90e73c7b4aa2733ca6cc3f9b72d1124bb
• https://git.kernel.org/stable/c/c7077f43f30d817d10a9f8245e51576ac114b2f0
• https://git.kernel.org/stable/c/f82f184874d2761ebaa60dccf577921a0dbb3810
• https://git.kernel.org/stable/c/0a69b6b3a026543bc215ccc866d0aea5579e6ce2
• https://git.kernel.org/stable/c/617d55b90e73c7b4aa2733ca6cc3f9b72d1124bb
• https://git.kernel.org/stable/c/c7077f43f30d817d10a9f8245e51576ac114b2f0
• https://git.kernel.org/stable/c/f82f184874d2761ebaa60dccf577921a0dbb3810