CVE-2024-53177 in Linux
Summary
by MITRE • 12/27/2024
In the Linux kernel, the following vulnerability has been resolved:
smb: prevent use-after-free due to open_cached_dir error paths
If open_cached_dir() encounters an error parsing the lease from the server, the error handling may race with receiving a lease break, resulting in open_cached_dir() freeing the cfid while the queued work is pending.
Update open_cached_dir() to drop refs rather than directly freeing the cfid.
Have cached_dir_lease_break(), cfids_laundromat_worker(), and invalidate_all_cached_dirs() clear has_lease immediately while still holding cfids->cfid_list_lock, and then use this to also simplify the reference counting in cfids_laundromat_worker() and invalidate_all_cached_dirs().
Fixes this KASAN splat (which manually injects an error and lease break in open_cached_dir()):
================================================================== BUG: KASAN: slab-use-after-free in smb2_cached_lease_break+0x27/0xb0 Read of size 8 at addr ffff88811cc24c10 by task kworker/3:1/65
CPU: 3 UID: 0 PID: 65 Comm: kworker/3:1 Not tainted 6.12.0-rc6-g255cf264e6e5-dirty #87 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 Workqueue: cifsiod smb2_cached_lease_break Call Trace: dump_stack_lvl+0x77/0xb0 print_report+0xce/0x660 kasan_report+0xd3/0x110 smb2_cached_lease_break+0x27/0xb0 process_one_work+0x50a/0xc50 worker_thread+0x2ba/0x530 kthread+0x17c/0x1c0 ret_from_fork+0x34/0x60 ret_from_fork_asm+0x1a/0x30
Allocated by task 2464: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 open_cached_dir+0xa7d/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
Freed by task 2464: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x51/0x70 kfree+0x174/0x520 open_cached_dir+0x97f/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
Last potentially related work creation: kasan_save_stack+0x33/0x60 __kasan_record_aux_stack+0xad/0xc0 insert_work+0x32/0x100 __queue_work+0x5c9/0x870 queue_work_on+0x82/0x90 open_cached_dir+0x1369/0x1fb0 smb2_query_path_info+0x43c/0x6e0 cifs_get_fattr+0x346/0xf10 cifs_get_inode_info+0x157/0x210 cifs_revalidate_dentry_attr+0x2d1/0x460 cifs_getattr+0x173/0x470 vfs_statx_path+0x10f/0x160 vfs_statx+0xe9/0x150 vfs_fstatat+0x5e/0xc0 __do_sys_newfstatat+0x91/0xf0 do_syscall_64+0x95/0x1a0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
The buggy address belongs to the object at ffff88811cc24c00 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 16 bytes inside of freed 1024-byte region [ffff88811cc24c00, ffff88811cc25000)
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Analysis
by VulDB Data Team • 01/21/2026
The vulnerability described in CVE-2024-53177 resides within the Linux kernel's SMB (Server Message Block) implementation, specifically affecting the cifs (Common Internet File System) subsystem. This flaw manifests as a use-after-free condition that occurs during the processing of cached directory operations, particularly when handling lease break notifications. The issue is rooted in the improper management of reference counting for cached file identifiers, or cfids, which are used to maintain state information about open directories in SMB sessions. When an error is encountered during the parsing of a lease from the SMB server, the error handling code may race with the processing of pending lease break work items, leading to a scenario where the cfid structure is freed while other kernel threads are still referencing it.
The technical core of the vulnerability lies in the race condition between the error path of open_cached_dir() and the lease break handling mechanism. The function open_cached_dir() is responsible for creating and managing cached directory entries, but when it fails to parse a lease, it may prematurely free the cfid structure. Meanwhile, a work item queued by the lease break mechanism is still pending execution, creating a window where the freed memory is accessed, resulting in a use-after-free error. The kernel's KASAN (Kernel Address Sanitizer) detection system captured this condition in a test scenario that manually injected both an error and a lease break, confirming the problematic race condition. This vulnerability is classified under CWE-415 as an improper handling of memory allocation and deallocation, specifically involving use-after-free conditions.
The operational impact of this vulnerability is significant for systems running Linux kernels with SMB client support, particularly those that frequently access SMB shares and rely on lease mechanisms for performance optimization. An attacker who can control or predict the timing of lease break notifications and error conditions in SMB server communications could potentially exploit this race condition to cause system instability, leading to kernel crashes, data corruption, or in more severe cases, privilege escalation. The vulnerability affects the cifs kernel module and is particularly concerning in enterprise environments where SMB shares are extensively used for file access and collaboration. The use-after-free condition can manifest as kernel oops messages, system panics, or more subtle memory corruption issues that may go unnoticed but compromise system integrity. This vulnerability aligns with ATT&CK technique T1059.001 for kernel-level code execution and T1566.001 for credential access through network protocols, making it a critical concern for system administrators and security teams monitoring Linux kernel security.
The fix implemented addresses the root cause by modifying the reference counting mechanism in the affected functions. Instead of directly freeing the cfid structure, the open_cached_dir() function now properly drops references to allow for safe cleanup by the reference counting system. Additionally, the cached_dir_lease_break(), cfids_laundromat_worker(), and invalidate_all_cached_dirs() functions now clear the has_lease flag immediately while holding the cfids->cfid_list_lock, ensuring atomicity in the state management. This approach eliminates the race condition by ensuring that all references to the cfid are properly managed before any freeing operations occur. The fix also simplifies the reference counting logic in the worker functions, reducing complexity and potential for similar issues. This solution follows established kernel security practices for handling concurrent access to shared data structures and aligns with the Linux kernel's memory management best practices. The mitigation effectively prevents the use-after-free condition by ensuring proper synchronization and reference counting throughout the SMB directory caching subsystem, thereby protecting against potential exploitation scenarios that could lead to system compromise.