CVE-2025-22121 in Linux
Summary
by MITRE • 04/16/2025
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix out-of-bound read in ext4_xattr_inode_dec_ref_all()
There's issue as follows: BUG: KASAN: use-after-free in ext4_xattr_inode_dec_ref_all+0x6ff/0x790 Read of size 4 at addr ffff88807b003000 by task syz-executor.0/15172
CPU: 3 PID: 15172 Comm: syz-executor.0 Call Trace: __dump_stack lib/dump_stack.c:82 [inline]
dump_stack+0xbe/0xfd lib/dump_stack.c:123 print_address_description.constprop.0+0x1e/0x280 mm/kasan/report.c:400 __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560 kasan_report+0x3a/0x50 mm/kasan/report.c:585 ext4_xattr_inode_dec_ref_all+0x6ff/0x790 fs/ext4/xattr.c:1137 ext4_xattr_delete_inode+0x4c7/0xda0 fs/ext4/xattr.c:2896 ext4_evict_inode+0xb3b/0x1670 fs/ext4/inode.c:323 evict+0x39f/0x880 fs/inode.c:622 iput_final fs/inode.c:1746 [inline]
iput fs/inode.c:1772 [inline]
iput+0x525/0x6c0 fs/inode.c:1758 ext4_orphan_cleanup fs/ext4/super.c:3298 [inline]
ext4_fill_super+0x8c57/0xba40 fs/ext4/super.c:5300 mount_bdev+0x355/0x410 fs/super.c:1446 legacy_get_tree+0xfe/0x220 fs/fs_context.c:611 vfs_get_tree+0x8d/0x2f0 fs/super.c:1576 do_new_mount fs/namespace.c:2983 [inline]
path_mount+0x119a/0x1ad0 fs/namespace.c:3316 do_mount+0xfc/0x110 fs/namespace.c:3329 __do_sys_mount fs/namespace.c:3540 [inline]
__se_sys_mount+0x219/0x2e0 fs/namespace.c:3514 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1
Memory state around the buggy address: ffff88807b002f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff88807b002f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffff88807b003000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ^ ffff88807b003080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff88807b003100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
Above issue happens as ext4_xattr_delete_inode() isn't check xattr is valid if xattr is in inode. To solve above issue call xattr_check_inode() check if xattr if valid in inode. In fact, we can directly verify in ext4_iget_extra_inode(), so that there is no divergent verification.
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Analysis
by VulDB Data Team • 02/15/2026
The vulnerability described in CVE-2025-22121 affects the Linux kernel's ext4 file system implementation and specifically targets the ext4_xattr_inode_dec_ref_all() function. This issue manifests as a use-after-free condition detected by Kernel Address Sanitizer KASAN, which indicates memory access violations that occur when code attempts to read from memory that has already been freed. The problematic read operation occurs at address ffff88807b003000 with a size of 4 bytes, suggesting that a pointer to an extended attribute inode is being dereferenced after the inode has been released, leading to potential information disclosure or system instability.
The call trace demonstrates a clear execution path from the kernel's mount subsystem through the extended attribute handling functions, ultimately reaching the problematic function ext4_xattr_inode_dec_ref_all(). The sequence begins with syz-executor.0 attempting to mount an ext4 filesystem, which triggers the extended attribute processing path that eventually leads to the use-after-free error. The memory state around the corrupted address shows all bytes set to 0xff, a common pattern for freed memory regions in kernel space, confirming that the memory has indeed been deallocated but is still being accessed. This memory corruption can result in unpredictable behavior, including system crashes, privilege escalation, or denial of service conditions that could be exploited by malicious actors.
This vulnerability aligns with CWE-416, Use After Free, which is a well-documented class of memory safety issues that occur when a program continues to use a pointer after the memory it points to has been freed. The flaw stems from inadequate validation within the ext4_xattr_delete_inode() function, which fails to verify that extended attributes are valid before attempting to decrement reference counts on them. The fix involves implementing proper validation checks by calling xattr_check_inode() to ensure that extended attributes are still valid in the inode context. This approach directly addresses the root cause by performing validation within ext4_iget_extra_inode(), eliminating divergent verification logic that could lead to inconsistent state management. The solution follows established security practices for kernel memory management and aligns with ATT&CK technique T1068, Exploitation for Privilege Escalation, by preventing potential exploitation paths that could arise from improper memory handling in kernel space. The vulnerability impacts system stability and security integrity, particularly in environments where extended attributes are heavily utilized, and requires immediate patching to prevent potential exploitation by adversaries seeking to compromise kernel-level security controls.