CVE-2026-64062 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix potential deadlock in write-through mode
Fix netfs_advance_writethrough() to always unlock the supplied folio and to mark it dirty if it isn't yet written to the end. Unfortunately, it can't be marked for writeback until the folio is done with as that may cause a deadlock against mmapped reads and writes.
Even though it has been marked dirty, premature writeback can't occur as the caller is holding both inode->i_rwsem (which will prevent concurrent truncation, fallocation, DIO and other writes) and ictx->wb_lock (which will cause flushing to wait and writeback to skip or wait).
Note that this may be easier to deal with once the queuing of folios is split from the generation of subrequests.
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Analysis
by VulDB Data Team • 07/19/2026
This vulnerability resides within the Linux kernel's network filesystem implementation where a potential deadlock scenario exists in write-through mode operations. The issue specifically affects the netfs_advance_writethrough() function which handles the advancement of data through network filesystems while maintaining write-through semantics. The flaw occurs when folios are not properly unlocked after processing, creating a deadlock condition that can prevent further I/O operations from proceeding. This type of vulnerability falls under CWE-362 which classifies concurrent execution using shared resources without proper synchronization mechanisms.
The technical implementation problem stems from improper resource management within the network filesystem subsystem where folios must be explicitly unlocked regardless of their write status. When a folio has not yet been written to its complete end, the function should mark it as dirty to ensure data persistence, but this marking must occur before releasing locks to prevent race conditions. The complexity arises because premature writeback operations cannot be initiated until the folio processing is complete, as doing so would create deadlock scenarios with memory-mapped read and write operations. This represents a classic deadlock avoidance pattern where multiple locking mechanisms must be coordinated properly.
The operational impact of this vulnerability can be significant in network filesystem environments where concurrent access patterns are common. Systems relying on network filesystems for storage operations may experience complete service unavailability or severe performance degradation when the deadlock condition occurs. The vulnerability affects the core I/O subsystem and can propagate through applications that depend on stable filesystem operations, potentially causing cascading failures in distributed systems. From an attack perspective, this could be exploited to create denial-of-service conditions against network filesystem servers or clients.
Mitigation strategies should focus on ensuring proper lock ordering and resource management within the network filesystem code path. The fix requires modifying the netfs_advance_writethrough() function to guarantee that folios are always unlocked after processing while maintaining appropriate dirty state flags. System administrators should monitor for potential performance impacts during kernel upgrades and consider implementing additional I/O monitoring to detect deadlock conditions. The solution aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, as this vulnerability could enable similar attack vectors through system resource exhaustion.
The fix implementation addresses the fundamental race condition by ensuring proper lock release semantics while maintaining data integrity guarantees. The approach recognizes that folio dirty flags can be set safely before writeback initiation, but actual writeback operations must wait until all concurrent access patterns are resolved to prevent deadlock conditions. This solution pattern demonstrates good practice in kernel development where complex locking scenarios require careful coordination between different subsystems. The suggested future enhancement of separating folio queuing from subrequest generation represents a more fundamental architectural improvement that would eliminate such race conditions at their source.
The vulnerability exemplifies the challenges inherent in kernel-level concurrent programming where multiple locking mechanisms must be orchestrated without creating circular dependencies. The specific locking context involving inode->i_rwsem and ictx->wb_lock demonstrates how different subsystems within the kernel must coordinate their locking strategies to prevent deadlocks. This type of issue commonly occurs in filesystem implementations where write-through semantics must be maintained while supporting concurrent access patterns from multiple processes and memory mappings. The fix maintains backward compatibility while eliminating the potential for system-wide deadlock conditions that could affect network filesystem availability.