CVE-2024-39291

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

drm/amdgpu: Fix buffer size in gfx_v9_4_3_init_ cp_compute_microcode() and rlc_microcode()

The function gfx_v9_4_3_init_microcode in gfx_v9_4_3.c was generating about potential truncation of output when using the snprintf function. The issue was due to the size of the buffer ucode_prefix being too small to accommodate the maximum possible length of the string being written into it.

The string being written is amdgpu/%s_mec.bin or amdgpu/%s_rlc.bin, where %s is replaced by the value of chip_name. The length of this string without the %s is 16 characters. The warning message indicated that chip_name could be up to 29 characters long, resulting in a total of 45 characters, which exceeds the buffer size of 30 characters.

To resolve this issue, the size of the ucode_prefix buffer has been reduced from 30 to 15. This ensures that the maximum possible length of the string being written into the buffer will not exceed its size, thus preventing potential buffer overflow and truncation issues.

Fixes the below with gcc W=1: drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c: In function ‘gfx_v9_4_3_early_init’: drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c:379:52: warning: ‘%s’ directive output may be truncated writing up to 29 bytes into a region of size 23 [-Wformat-truncation=] 379 | snprintf(fw_name, sizeof(fw_name), amdgpu/%s_rlc.bin, chip_name); | ^~ …… 439 | r = gfx_v9_4_3_init_rlc_microcode(adev, ucode_prefix); | ~~~~~~~~~~~~ drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c:379:9: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 30 379 | snprintf(fw_name, sizeof(fw_name), amdgpu/%s_rlc.bin, chip_name); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c:413:52: warning: ‘%s’ directive output may be truncated writing up to 29 bytes into a region of size 23 [-Wformat-truncation=] 413 | snprintf(fw_name, sizeof(fw_name), amdgpu/%s_mec.bin, chip_name); | ^~ …… 443 | r = gfx_v9_4_3_init_cp_compute_microcode(adev, ucode_prefix); | ~~~~~~~~~~~~ drivers/gpu/drm/amd/amdgpu/gfx_v9_4_3.c:413:9: note: ‘snprintf’ output between 16 and 45 bytes into a destination of size 30 413 | snprintf(fw_name, sizeof(fw_name), amdgpu/%s_mec.bin, chip_name); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Weakness

The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow.

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:

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”

• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

• 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].

• Run the code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.

• OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.

• This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.

• Be careful to avoid CWE-243 and other weaknesses related to jails.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/10.html
• https://cwe.mitre.org/data/definitions/100.html
• https://cwe.mitre.org/data/definitions/14.html
• https://cwe.mitre.org/data/definitions/24.html
• https://cwe.mitre.org/data/definitions/42.html
• https://cwe.mitre.org/data/definitions/44.html
• https://cwe.mitre.org/data/definitions/45.html
• https://cwe.mitre.org/data/definitions/46.html
• https://cwe.mitre.org/data/definitions/47.html
• https://cwe.mitre.org/data/definitions/67.html
• https://cwe.mitre.org/data/definitions/8.html
• https://cwe.mitre.org/data/definitions/9.html
• https://cwe.mitre.org/data/definitions/92.html

References

• https://git.kernel.org/stable/c/19bd9537b6bc1c882df25206c15917214d8e9460
• https://git.kernel.org/stable/c/acce6479e30f73ab0872e93a75aed1fb791d04ec
• https://git.kernel.org/stable/c/f1b6a016dfa45cedc080d36fa5d6f22237d80e8b