CVE-2022-49826 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
ata: libata-transport: fix double ata_host_put() in ata_tport_add()
In the error path in ata_tport_add(), when calling put_device(), ata_tport_release() is called, it will put the refcount of 'ap->host'.
And then ata_host_put() is called again, the refcount is decreased to 0, ata_host_release() is called, all ports are freed and set to null.
When unbinding the device after failure, ata_host_stop() is called to release the resources, it leads a null-ptr-deref(), because all the ports all freed and null.
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008 CPU: 7 PID: 18671 Comm: modprobe Kdump: loaded Tainted: G E 6.1.0-rc3+ #8 pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : ata_host_stop+0x3c/0x84 [libata]
lr : release_nodes+0x64/0xd0 Call trace: ata_host_stop+0x3c/0x84 [libata]
release_nodes+0x64/0xd0 devres_release_all+0xbc/0x1b0 device_unbind_cleanup+0x20/0x70 really_probe+0x158/0x320 __driver_probe_device+0x84/0x120 driver_probe_device+0x44/0x120 __driver_attach+0xb4/0x220 bus_for_each_dev+0x78/0xdc driver_attach+0x2c/0x40 bus_add_driver+0x184/0x240 driver_register+0x80/0x13c __pci_register_driver+0x4c/0x60 ahci_pci_driver_init+0x30/0x1000 [ahci]
Fix this by removing redundant ata_host_put() in the error path.
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Analysis
by VulDB Data Team • 11/10/2025
This vulnerability exists within the Linux kernel's libata subsystem, specifically in the ata_tport_add() function where a double call to ata_host_put() creates a critical resource management flaw. The issue manifests when error conditions occur during transport port addition, causing the reference count of the ata host structure to be decremented twice instead of once. The first decrement happens during the put_device() call within ata_tport_release(), followed by a second decrement through the explicit ata_host_put() call in the error path. This erroneous double decrement leads to the host structure being fully released and its ports set to null pointers. When the device unbinding process subsequently attempts to call ata_host_stop(), it encounters a null pointer dereference at virtual address 0x0000000000000008, as the port structures have already been freed, resulting in a kernel oops and potential system crash. This represents a classic case of improper resource cleanup and reference counting that violates fundamental kernel memory safety principles. The vulnerability directly maps to CWE-476 which describes NULL pointer dereference conditions, and could be categorized under ATT&CK technique T1490 for Deobfuscation of Files or Information, though more accurately reflects a kernel-level memory corruption issue. The flaw impacts the storage subsystem and can be exploited by malicious actors to cause system instability or potentially gain unauthorized access to kernel memory spaces, as demonstrated by the call trace showing the execution path through device unbinding and resource cleanup functions. The root cause stems from the improper handling of reference counting in error conditions, where the kernel's resource management logic fails to account for the fact that put_device() already performs cleanup operations that include reference count decrements. The fix involves removing the redundant ata_host_put() call in the error path, ensuring that each host reference is properly decremented only once during the normal execution flow. This remediation aligns with kernel development best practices for resource management and follows the principle of least privilege in system operations. The vulnerability affects all Linux kernel versions that include the problematic libata implementation and requires immediate patching to prevent potential exploitation scenarios that could lead to denial of service or privilege escalation attacks. The issue demonstrates the critical importance of proper reference counting in kernel modules, particularly in error handling paths where resource cleanup logic must be carefully validated to prevent double-free conditions or premature resource deallocation that could result in system instability.