CVE-2021-47288

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

media: ngene: Fix out-of-bounds bug in ngene_command_config_free_buf()

Fix an 11-year old bug in ngene_command_config_free_buf() while addressing the following warnings caught with -Warray-bounds:

arch/alpha/include/asm/string.h:22:16: warning: __builtin_memcpy offset [12, 16] from the object at com is out of the bounds of referenced subobject config with type unsigned char at offset 10 [-Warray-bounds] arch/x86/include/asm/string_32.h:182:25: warning: __builtin_memcpy offset [12, 16] from the object at com is out of the bounds of referenced subobject config with type unsigned char at offset 10 [-Warray-bounds]

The problem is that the original code is trying to copy 6 bytes of data into a one-byte size member config of the wrong structue FW_CONFIGURE_BUFFERS, in a single call to memcpy(). This causes a legitimate compiler warning because memcpy() overruns the length of &com.cmd.ConfigureBuffers.config. It seems that the right structure is FW_CONFIGURE_FREE_BUFFERS, instead, because it contains 6 more members apart from the header hdr. Also, the name of the function ngene_command_config_free_buf() suggests that the actual intention is to ConfigureFreeBuffers, instead of ConfigureBuffers (which takes place in the function ngene_command_config_buf(), above).

Fix this by enclosing those 6 members of struct FW_CONFIGURE_FREE_BUFFERS into new struct config, and use &com.cmd.ConfigureFreeBuffers.config as the destination address, instead of &com.cmd.ConfigureBuffers.config, when calling memcpy().

This also helps with the ongoing efforts to globally enable -Warray-bounds and get us closer to being able to tighten the FORTIFY_SOURCE routines on memcpy().

Weakness

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

Affected Software

Potential Mitigations

• 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.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/4487b968e5eacd02c493303dc2b61150bb7fe4b2
• https://git.kernel.org/stable/c/8d4abca95ecc82fc8c41912fa0085281f19cc29f
• https://git.kernel.org/stable/c/b9a178f189bb6d75293573e181928735f5e3e070
• https://git.kernel.org/stable/c/c6ddeb63dd543b5474b0217c4e47538b7ffd7686
• https://git.kernel.org/stable/c/e617fa62f6cf859a7b042cdd6c73af905ff8fca3
• https://git.kernel.org/stable/c/e818f2ff648581a6c553ae2bebc5dcef9a8bb90c
• https://git.kernel.org/stable/c/e991457afdcb5f4dbc5bc9d79eaf775be33e7092
• https://git.kernel.org/stable/c/ec731c6ef564ee6fc101fc5d73e3a3a953d09a00
• https://git.kernel.org/stable/c/4487b968e5eacd02c493303dc2b61150bb7fe4b2
• https://git.kernel.org/stable/c/8d4abca95ecc82fc8c41912fa0085281f19cc29f
• https://git.kernel.org/stable/c/b9a178f189bb6d75293573e181928735f5e3e070
• https://git.kernel.org/stable/c/c6ddeb63dd543b5474b0217c4e47538b7ffd7686
• https://git.kernel.org/stable/c/e617fa62f6cf859a7b042cdd6c73af905ff8fca3
• https://git.kernel.org/stable/c/e818f2ff648581a6c553ae2bebc5dcef9a8bb90c
• https://git.kernel.org/stable/c/e991457afdcb5f4dbc5bc9d79eaf775be33e7092
• https://git.kernel.org/stable/c/ec731c6ef564ee6fc101fc5d73e3a3a953d09a00