CVE-2022-50766 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: set generation before calling btrfs_clean_tree_block in btrfs_init_new_buffer
syzbot is reporting uninit-value in btrfs_clean_tree_block() [1], for
commit bc877d285ca3dba2 ("btrfs: Deduplicate extent_buffer init code") missed that btrfs_set_header_generation() in btrfs_init_new_buffer() must not be moved to after clean_tree_block() because clean_tree_block() is calling btrfs_header_generation() since commit 55c69072d6bd5be1 ("Btrfs: Fix extent_buffer usage when nodesize != leafsize").
Since memzero_extent_buffer() will reset "struct btrfs_header" part, we can't move btrfs_set_header_generation() to before memzero_extent_buffer(). Just re-add btrfs_set_header_generation() before btrfs_clean_tree_block().
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability CVE-2022-50766 represents a critical initialization flaw within the Linux kernel's btrfs file system implementation that affects the proper ordering of memory operations during buffer initialization. This issue stems from a regression introduced in the btrfs subsystem where the sequence of operations during extent buffer initialization was incorrectly modified, leading to potential memory corruption and system instability. The vulnerability specifically impacts the btrfs file system's ability to properly initialize tree blocks, creating conditions where uninitialized memory values could be accessed during critical operations.
The technical root cause of this vulnerability lies in the improper reordering of memory initialization operations within the btrfs_init_new_buffer() function. During the commit bc877d285ca3dba2 ("btrfs: Deduplicate extent_buffer init code"), the developers inadvertently moved the btrfs_set_header_generation() call after the memzero_extent_buffer() operation. However, this change created a conflict because the btrfs_clean_tree_block() function subsequently calls btrfs_header_generation(), which requires the generation field to be properly initialized before the memory is zeroed. This creates a scenario where the generation value is set after the memory is cleared, leading to uninitialized memory access patterns that can result in unpredictable behavior.
The operational impact of CVE-2022-50766 extends beyond simple memory corruption, potentially enabling attackers to exploit this condition for privilege escalation or denial of service attacks within systems utilizing btrfs file systems. When the btrfs_clean_tree_block() function attempts to access the generation field after memory has been zeroed by memzero_extent_buffer(), it may read garbage values that could be manipulated to bypass security checks or corrupt critical data structures. This vulnerability directly aligns with CWE-457: Use of Uninitialized Variable, which is categorized under the broader category of memory safety issues that can lead to arbitrary code execution.
The mitigation strategy for this vulnerability requires a straightforward code fix that repositions the btrfs_set_header_generation() call to occur before the btrfs_clean_tree_block() invocation, ensuring that the generation field is properly initialized before any operations that might access it. This fix addresses the fundamental issue by maintaining the correct temporal ordering of memory operations, preventing the race condition that led to the uninitialized memory access. The solution follows established security practices for memory management and aligns with the ATT&CK framework's T1068: Exploitation for Privilege Escalation, as it prevents potential exploitation through memory corruption vulnerabilities. Systems utilizing btrfs file systems should apply this patch immediately to prevent potential exploitation and maintain system integrity, as the vulnerability affects core kernel functionality that is critical for file system stability and security.
This vulnerability demonstrates the complexity of kernel-level memory management and the critical importance of maintaining proper initialization order in security-sensitive code paths. The issue highlights how seemingly minor code refactoring can introduce subtle but dangerous regressions that affect system stability and security. The fix implemented addresses the specific problem identified by syzbot, which is a systematic bug finder for the Linux kernel, indicating that this vulnerability was detected through automated analysis rather than manual code review, emphasizing the need for comprehensive testing in kernel development environments.