CVE-2024-26972 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
ubifs: ubifs_symlink: Fix memleak of inode->i_link in error path
For error handling path in ubifs_symlink(), inode will be marked as bad first, then iput() is invoked. If inode->i_link is initialized by fscrypt_encrypt_symlink() in encryption scenario, inode->i_link won't be freed by callchain ubifs_free_inode -> fscrypt_free_inode in error handling path, because make_bad_inode() has changed 'inode->i_mode' as 'S_IFREG'. Following kmemleak is easy to be reproduced by injecting error in ubifs_jnl_update() when doing symlink in encryption scenario: unreferenced object 0xffff888103da3d98 (size 8): comm "ln", pid 1692, jiffies 4294914701 (age 12.045s) backtrace: kmemdup+0x32/0x70 __fscrypt_encrypt_symlink+0xed/0x1c0 ubifs_symlink+0x210/0x300 [ubifs]
vfs_symlink+0x216/0x360 do_symlinkat+0x11a/0x190 do_syscall_64+0x3b/0xe0 There are two ways fixing it: 1. Remove make_bad_inode() in error handling path. We can do that because ubifs_evict_inode() will do same processes for good symlink inode and bad symlink inode, for inode->i_nlink checking is before is_bad_inode(). 2. Free inode->i_link before marking inode bad. Method 2 is picked, it has less influence, personally, I think.
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Analysis
by VulDB Data Team • 05/22/2026
The vulnerability exists within the Linux kernel's UBIFS (Unsorted Block Images File System) implementation, specifically in the symlink creation functionality where a memory leak occurs during error handling scenarios. This issue manifests when the ubifs_symlink() function encounters an error condition while processing symbolic links in encrypted filesystem scenarios. The root cause stems from the improper ordering of operations within the error path where inode cleanup procedures fail to properly release allocated resources.
The technical flaw occurs because when an error occurs during symlink creation in an encryption context, the function first invokes make_bad_inode() which modifies the inode's mode from its original value to S_IFREG, effectively changing the inode's classification. This modification prevents the normal cleanup chain from executing properly, specifically the fscrypt_free_inode function that would normally free the inode->i_link field. The fscrypt_encrypt_symlink() function has already initialized inode->i_link during the encryption process, but this memory allocation remains unreleased when make_bad_inode() alters the inode's mode, breaking the expected cleanup sequence.
The operational impact of this vulnerability is significant as it creates persistent memory leaks that accumulate over time, potentially leading to system performance degradation and resource exhaustion. The kmemleak detection mechanism easily identifies this issue by injecting errors during ubifs_jnl_update() operations, demonstrating how the memory leak occurs when creating symbolic links in encrypted filesystem scenarios. The backtrace shows the call chain from kmemdup through fscrypt_encrypt_symlink to ubifs_symlink, highlighting the precise sequence where memory allocation occurs without proper cleanup.
The vulnerability aligns with CWE-401 (Improper Release of Memory Before Removal from Managed List) and relates to ATT&CK technique T1484 (Domain Policy Modification) through potential system stability impacts. The fix implements method two, which involves freeing inode->i_link before marking the inode as bad, minimizing disruption to existing functionality. This approach ensures proper resource cleanup regardless of the inode's mode state while maintaining the integrity of the error handling process. The solution addresses the core issue by ensuring that encryption-related memory allocations are properly released before the inode state modification occurs, preventing the memory leak from occurring in error conditions.
The fix demonstrates proper defensive programming practices by ensuring that all allocated resources are freed before state changes that might interfere with cleanup procedures. This approach maintains the filesystem's ability to properly handle error conditions while preserving the security benefits of encryption. The implementation follows established kernel development practices for managing resource cleanup in error paths, ensuring that the filesystem maintains both reliability and security properties even under adverse conditions.