CVE-2023-52751

In the Linux kernel, the following vulnerability has been resolved:

smb: client: fix use-after-free in smb2_query_info_compound()

The following UAF was triggered when running fstests generic/072 with KASAN enabled against Windows Server 2022 and mount options multichannel,max_channels=2,vers=3.1.1,mfsymlinks,noperm

BUG: KASAN: slab-use-after-free in smb2_query_info_compound+0x423/0x6d0 [cifs] Read of size 8 at addr ffff888014941048 by task xfs_io/27534

CPU: 0 PID: 27534 Comm: xfs_io Not tainted 6.6.0-rc7 #1 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014 Call Trace: dump_stack_lvl+0x4a/0x80 print_report+0xcf/0x650 ? srso_alias_return_thunk+0x5/0x7f ? srso_alias_return_thunk+0x5/0x7f ? __phys_addr+0x46/0x90 kasan_report+0xda/0x110 ? smb2_query_info_compound+0x423/0x6d0 [cifs] ? smb2_query_info_compound+0x423/0x6d0 [cifs] smb2_query_info_compound+0x423/0x6d0 [cifs] ? __pfx_smb2_query_info_compound+0x10/0x10 [cifs] ? srso_alias_return_thunk+0x5/0x7f ? __stack_depot_save+0x39/0x480 ? kasan_save_stack+0x33/0x60 ? kasan_set_track+0x25/0x30 ? ____kasan_slab_free+0x126/0x170 smb2_queryfs+0xc2/0x2c0 [cifs] ? __pfx_smb2_queryfs+0x10/0x10 [cifs] ? __pfx___lock_acquire+0x10/0x10 smb311_queryfs+0x210/0x220 [cifs] ? __pfx_smb311_queryfs+0x10/0x10 [cifs] ? srso_alias_return_thunk+0x5/0x7f ? __lock_acquire+0x480/0x26c0 ? lock_release+0x1ed/0x640 ? srso_alias_return_thunk+0x5/0x7f ? do_raw_spin_unlock+0x9b/0x100 cifs_statfs+0x18c/0x4b0 [cifs] statfs_by_dentry+0x9b/0xf0 fd_statfs+0x4e/0xb0 __do_sys_fstatfs+0x7f/0xe0 ? __pfx___do_sys_fstatfs+0x10/0x10 ? srso_alias_return_thunk+0x5/0x7f ? lockdep_hardirqs_on_prepare+0x136/0x200 ? srso_alias_return_thunk+0x5/0x7f do_syscall_64+0x3f/0x90 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Allocated by task 27534: kasan_save_stack+0x33/0x60 kasan_set_track+0x25/0x30 __kasan_kmalloc+0x8f/0xa0 open_cached_dir+0x71b/0x1240 [cifs] smb2_query_info_compound+0x5c3/0x6d0 [cifs] smb2_queryfs+0xc2/0x2c0 [cifs] smb311_queryfs+0x210/0x220 [cifs] cifs_statfs+0x18c/0x4b0 [cifs] statfs_by_dentry+0x9b/0xf0 fd_statfs+0x4e/0xb0 __do_sys_fstatfs+0x7f/0xe0 do_syscall_64+0x3f/0x90 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

Freed by task 27534: kasan_save_stack+0x33/0x60 kasan_set_track+0x25/0x30 kasan_save_free_info+0x2b/0x50 ____kasan_slab_free+0x126/0x170 slab_free_freelist_hook+0xd0/0x1e0 __kmem_cache_free+0x9d/0x1b0 open_cached_dir+0xff5/0x1240 [cifs] smb2_query_info_compound+0x5c3/0x6d0 [cifs] smb2_queryfs+0xc2/0x2c0 [cifs]

This is a race between open_cached_dir() and cached_dir_lease_break() where the cache entry for the open directory handle receives a lease break while creating it. And before returning from open_cached_dir(), we put the last reference of the new @cfid because of !@cfid->has_lease.

Besides the UAF, while running xfstests a lot of missed lease breaks have been noticed in tests that run several concurrent statfs(2) calls on those cached fids

CIFS: VFS: w22-root1.gandalf.test No task to wake, unknown frame… CIFS: VFS: w22-root1.gandalf.test Cmd: 18 Err: 0x0 Flags: 0x1… CIFS: VFS: w22-root1.gandalf.test smb buf 00000000715bfe83 len 108 CIFS: VFS: Dump pending requests: CIFS: VFS: w22-root1.gandalf.test No task to wake, unknown frame… CIFS: VFS: w22-root1.gandalf.test Cmd: 18 Err: 0x0 Flags: 0x1… CIFS: VFS: w22-root1.gandalf.test smb buf 000000005aa7316e len 108 …

To fix both, in open_cached_dir() ensure that @cfid->has_lease is set right before sending out compounded request so that any potential lease break will be get processed by demultiplex thread while were still caching @cfid. And, if open failed for some reason, re-check @cfid->has_lease to decide whether or not put lease reference.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/5c86919455c1edec99ebd3338ad213b59271a71b
• https://git.kernel.org/stable/c/6db94d08359c43f2c8fe372811cdee04564a41b9
• https://git.kernel.org/stable/c/93877b9afc2994c89362007aac480a7b150f386f
• https://git.kernel.org/stable/c/5c86919455c1edec99ebd3338ad213b59271a71b
• https://git.kernel.org/stable/c/6db94d08359c43f2c8fe372811cdee04564a41b9
• https://git.kernel.org/stable/c/93877b9afc2994c89362007aac480a7b150f386f