CVE-2024-26972

Published: 1 May 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.

From the Ubuntu Security Team

A memory leak is found in the ubifs subsystem when a certain error occurs, leading to potential denial of service and harming the system's confidentiality.

Notes

The fix commit is applied twice, 1e022216dcd2 and 6379b44cdcd6, and the upstream has decided to revert the latter one keep the first one. So use the first one instead of the second one.

Status

References

• https://www.cve.org/CVERecord?id=CVE-2024-26972
• https://git.kernel.org/linus/6379b44cdcd67f5f5d986b73953e99700591edfa (6.9-rc1)
• https://git.kernel.org/stable/c/62b5ae00c2b835639002ce898ccb5d82c51073ae
• https://git.kernel.org/stable/c/6379b44cdcd67f5f5d986b73953e99700591edfa
• https://ubuntu.com/security/notices/USN-6816-1
• https://ubuntu.com/security/notices/USN-6817-1
• https://ubuntu.com/security/notices/USN-6817-2
• https://ubuntu.com/security/notices/USN-6817-3
• https://ubuntu.com/security/notices/USN-6878-1
• NVD
• Launchpad
• Debian