CVE-2022-50406

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

iomap: iomap: fix memory corruption when recording errors during writeback

Every now and then I see this crash on arm64:

Unable to handle kernel NULL pointer dereference at virtual address 00000000000000f8 Buffer I/O error on dev dm-0, logical block 8733687, async page read Mem abort info: ESR = 0x0000000096000006 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x06: level 2 translation fault Data abort info: ISV = 0, ISS = 0x00000006 CM = 0, WnR = 0 user pgtable: 64k pages, 42-bit VAs, pgdp=0000000139750000 [00000000000000f8] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000, pmd=0000000000000000 Internal error: Oops: 96000006 [#1] PREEMPT SMP Buffer I/O error on dev dm-0, logical block 8733688, async page read Dumping ftrace buffer: Buffer I/O error on dev dm-0, logical block 8733689, async page read (ftrace buffer empty) XFS (dm-0): log I/O error -5 Modules linked in: dm_thin_pool dm_persistent_data XFS (dm-0): Metadata I/O Error (0x1) detected at xfs_trans_read_buf_map+0x1ec/0x590 [xfs] (fs/xfs/xfs_trans_buf.c:296). dm_bio_prison XFS (dm-0): Please unmount the filesystem and rectify the problem(s) XFS (dm-0): xfs_imap_lookup: xfs_ialloc_read_agi() returned error -5, agno 0 dm_bufio dm_log_writes xfs nft_chain_nat xt_REDIRECT nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip6t_REJECT potentially unexpected fatal signal 6. nf_reject_ipv6 potentially unexpected fatal signal 6. ipt_REJECT nf_reject_ipv4 CPU: 1 PID: 122166 Comm: fsstress Tainted: G W 6.0.0-rc5-djwa #rc5 3004c9f1de887ebae86015f2677638ce51ee7 rpcsec_gss_krb5 auth_rpcgss xt_tcpudp ip_set_hash_ip ip_set_hash_net xt_set nft_compat ip_set_hash_mac ip_set nf_tables Hardware name: QEMU KVM Virtual Machine, BIOS 1.5.1 06/16/2021 pstate: 60001000 (nZCv daif -PAN -UAO -TCO -DIT +SSBS BTYPE=–) ip_tables pc : 000003fd6d7df200 x_tables lr : 000003fd6d7df1ec overlay nfsv4 CPU: 0 PID: 54031 Comm: u4:3 Tainted: G W 6.0.0-rc5-djwa #rc5 3004c9f1de887ebae86015f2677638ce51ee7405 Hardware name: QEMU KVM Virtual Machine, BIOS 1.5.1 06/16/2021 Workqueue: writeback wb_workfn sp : 000003ffd9522fd0 (flush-253:0) pstate: 60401005 (nZCv daif +PAN -UAO -TCO -DIT +SSBS BTYPE=–) pc : errseq_set+0x1c/0x100 x29: 000003ffd9522fd0 x28: 0000000000000023 x27: 000002acefeb6780 x26: 0000000000000005 x25: 0000000000000001 x24: 0000000000000000 x23: 00000000ffffffff x22: 0000000000000005 lr : __filemap_set_wb_err+0x24/0xe0 x21: 0000000000000006 sp : fffffe000f80f760 x29: fffffe000f80f760 x28: 0000000000000003 x27: fffffe000f80f9f8 x26: 0000000002523000 x25: 00000000fffffffb x24: fffffe000f80f868 x23: fffffe000f80fbb0 x22: fffffc0180c26a78 x21: 0000000002530000 x20: 0000000000000000 x19: 0000000000000000 x18: 0000000000000000

x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000001 x13: 0000000000470af3 x12: fffffc0058f70000 x11: 0000000000000040 x10: 0000000000001b20 x9 : fffffe000836b288 x8 : fffffc00eb9fd480 x7 : 0000000000f83659 x6 : 0000000000000000 x5 : 0000000000000869 x4 : 0000000000000005 x3 : 00000000000000f8 x20: 000003fd6d740020 x19: 000000000001dd36 x18: 0000000000000001 x17: 000003fd6d78704c x16: 0000000000000001 x15: 000002acfac87668 x2 : 0000000000000ffa x1 : 00000000fffffffb x0 : 00000000000000f8 Call trace: errseq_set+0x1c/0x100 __filemap_set_wb_err+0x24/0xe0 iomap_do_writepage+0x5e4/0xd5c write_cache_pages+0x208/0x674 iomap_writepages+0x34/0x60 xfs_vm_writepages+0x8c/0xcc [xfs 7a861f39c43631f15d3a5884246ba5035d4ca78b] x14: 0000000000000000 x13: 2064656e72757465 x12: 0000000000002180 x11: 000003fd6d8a82d0 x10: 0000000000000000 x9 : 000003fd6d8ae288 x8 : 0000000000000083 x7 : 00000000ffffffff x6 : 00000000ffffffee x5 : 00000000fbad2887 x4 : 000003fd6d9abb58 x3 : 000003fd6d740020 x2 : 0000000000000006 x1 : 000000000001dd36 x0 : 0000000000000000 CPU: —truncated—

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/3d5f3ba1ac28059bdf7000cae2403e4e984308d2
• https://git.kernel.org/stable/c/7308591d9c7787aec58f6a01a7823f14e90db7a2
• https://git.kernel.org/stable/c/82c66c46f73b88be74c869e2cbfef45281adf3c6