CVE-2021-47458

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

ocfs2: mount fails with buffer overflow in strlen

Starting with kernel 5.11 built with CONFIG_FORTIFY_SOURCE mouting an ocfs2 filesystem with either o2cb or pcmk cluster stack fails with the trace below. Problem seems to be that strings for cluster stack and cluster name are not guaranteed to be null terminated in the disk representation, while strlcpy assumes that the source string is always null terminated. This causes a read outside of the source string triggering the buffer overflow detection.

detected buffer overflow in strlen ————[ cut here ]———— kernel BUG at lib/string.c:1149! invalid opcode: 0000 [#1] SMP PTI CPU: 1 PID: 910 Comm: mount.ocfs2 Not tainted 5.14.0-1-amd64 #1 Debian 5.14.6-2 RIP: 0010:fortify_panic+0xf/0x11 … Call Trace: ocfs2_initialize_super.isra.0.cold+0xc/0x18 [ocfs2] ocfs2_fill_super+0x359/0x19b0 [ocfs2] mount_bdev+0x185/0x1b0 legacy_get_tree+0x27/0x40 vfs_get_tree+0x25/0xb0 path_mount+0x454/0xa20 __x64_sys_mount+0x103/0x140 do_syscall_64+0x3b/0xc0 entry_SYSCALL_64_after_hwframe+0x44/0xae

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/0e677ea5b7396f715a76b6b0ef441430e4c4b57f
• https://git.kernel.org/stable/c/232ed9752510de4436468b653d145565669c8498
• https://git.kernel.org/stable/c/4b74ddcc22ee6455946e80a9c4808801f8f8561e
• https://git.kernel.org/stable/c/7623b1035ca2d17bde0f6a086ad6844a34648df1
• https://git.kernel.org/stable/c/93be0eeea14cf39235e585c8f56df3b3859deaad
• https://git.kernel.org/stable/c/ac011cb3ff7a76b3e0e6e77158ee4ba2f929e1fb
• https://git.kernel.org/stable/c/b15fa9224e6e1239414525d8d556d824701849fc
• https://git.kernel.org/stable/c/d3a83576378b4c904f711598dde2c5e881c4295c
• https://git.kernel.org/stable/c/0e677ea5b7396f715a76b6b0ef441430e4c4b57f
• https://git.kernel.org/stable/c/232ed9752510de4436468b653d145565669c8498
• https://git.kernel.org/stable/c/4b74ddcc22ee6455946e80a9c4808801f8f8561e
• https://git.kernel.org/stable/c/7623b1035ca2d17bde0f6a086ad6844a34648df1
• https://git.kernel.org/stable/c/93be0eeea14cf39235e585c8f56df3b3859deaad
• https://git.kernel.org/stable/c/ac011cb3ff7a76b3e0e6e77158ee4ba2f929e1fb
• https://git.kernel.org/stable/c/b15fa9224e6e1239414525d8d556d824701849fc
• https://git.kernel.org/stable/c/d3a83576378b4c904f711598dde2c5e881c4295c