CVE-2017-18257 in Linux
Summary
by MITRE
The __get_data_block function in fs/f2fs/data.c in the Linux kernel before 4.11 allows local users to cause a denial of service (integer overflow and loop) via crafted use of the open and fallocate system calls with an FS_IOC_FIEMAP ioctl.
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Analysis
by VulDB Data Team • 09/14/2025
The vulnerability identified as CVE-2017-18257 resides within the Linux kernel's F2FS (Flash-Friendly File System) implementation, specifically in the __get_data_block function located in fs/f2fs/data.c. This flaw represents a critical security issue that affects Linux kernel versions prior to 4.11, creating a pathway for local attackers to execute denial of service attacks through carefully crafted system call sequences. The vulnerability manifests when the open and fallocate system calls are combined with the FS_IOC_FIEMAP ioctl command, exploiting a fundamental flaw in how the kernel handles data block allocation and management.
The technical root cause of this vulnerability stems from an integer overflow condition that occurs within the data block processing logic. When a local user executes the specified combination of system calls, the kernel's handling of file allocation parameters causes integer arithmetic to exceed the maximum representable value for the data type being used. This overflow condition results in a loop that operates with incorrect parameters, causing the kernel to enter an infinite or extremely long-running loop. The integer overflow creates a scenario where the loop counter becomes negative or wraps around to a large positive value, leading to excessive resource consumption and system instability. This type of vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions that can lead to unpredictable behavior and system resource exhaustion.
The operational impact of this vulnerability extends beyond simple denial of service, as it can severely compromise system stability and availability. Local attackers can exploit this flaw to consume excessive CPU cycles and memory resources, effectively rendering the system unresponsive to legitimate user requests. The vulnerability is particularly dangerous because it requires minimal privileges to exploit, making it accessible to any local user with basic system access. The loop behavior created by the integer overflow can persist for extended periods, potentially causing the system to become unresponsive or crash entirely, depending on the system's resource constraints and the specific parameters used in the attack vector.
From a threat modeling perspective, this vulnerability fits within the ATT&CK framework under the T1499 category of Network Denial of Service, though it operates at the kernel level rather than network protocols. The attack vector requires local system access but does not require elevated privileges, making it particularly concerning for multi-user systems where users might have varying levels of access. The exploitation process involves crafting specific file operations that trigger the integer overflow, which then causes the kernel to enter an inefficient loop state. Security professionals should note that this vulnerability represents a classic example of how seemingly benign system calls can be combined to create dangerous conditions when proper input validation and overflow protection are absent from kernel code.
Mitigation strategies for CVE-2017-18257 primarily involve upgrading to Linux kernel version 4.11 or later, where the vulnerability has been patched through improved input validation and integer overflow protection mechanisms. System administrators should also implement monitoring solutions to detect unusual CPU and memory usage patterns that might indicate exploitation attempts. The patch for this vulnerability typically involves adding proper bounds checking to the integer operations and ensuring that loop parameters are validated before execution. Organizations should prioritize patching this vulnerability as part of their regular security maintenance procedures, particularly in environments where local access is not strictly controlled. Additionally, implementing proper system hardening measures and monitoring for anomalous system behavior can provide early detection capabilities for potential exploitation attempts.