CVE-2022-50279

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

wifi: rtlwifi: Fix global-out-of-bounds bug in _rtl8812ae_phy_set_txpower_limit()

There is a global-out-of-bounds reported by KASAN:

BUG: KASAN: global-out-of-bounds in _rtl8812ae_eq_n_byte.part.0+0x3d/0x84 [rtl8821ae] Read of size 1 at addr ffffffffa0773c43 by task NetworkManager/411

CPU: 6 PID: 411 Comm: NetworkManager Tainted: G D 6.1.0-rc8+ #144 e15588508517267d37 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), Call Trace: … kasan_report+0xbb/0x1c0 _rtl8812ae_eq_n_byte.part.0+0x3d/0x84 [rtl8821ae] rtl8821ae_phy_bb_config.cold+0x346/0x641 [rtl8821ae] rtl8821ae_hw_init+0x1f5e/0x79b0 [rtl8821ae] …

The root cause of the problem is that the comparison order of prate_section in _rtl8812ae_phy_set_txpower_limit() is wrong. The _rtl8812ae_eq_n_byte() is used to compare the first n bytes of the two strings from tail to head, which causes the problem. In the _rtl8812ae_phy_set_txpower_limit(), it was originally intended to meet this requirement by carefully designing the comparison order. For example, pregulation and pbandwidth are compared in order of length from small to large, first is 3 and last is 4. However, the comparison order of prate_section dose not obey such order requirement, therefore when prate_section is HT, when comparing from tail to head, it will lead to access out of bounds in _rtl8812ae_eq_n_byte(). As mentioned above, the _rtl8812ae_eq_n_byte() has the same function as strcmp(), so just strcmp() is enough.

Fix it by removing _rtl8812ae_eq_n_byte() and use strcmp() barely. Although it can be fixed by adjusting the comparison order of prate_section, this may cause the value of rate_section to not be from 0 to 5. In addition, commit 21e4b0726dc6 not only moved driver from staging to regular tree, but also added setting txpower limit function during the driver config phase, so the problem was introduced by this commit.

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/057b52461dc005ecd85a3e4998913b1492ec0f72
• https://git.kernel.org/stable/c/0c962dcd6bf64b78eaffc09e497a2beb4e48bc32
• https://git.kernel.org/stable/c/117dbeda22ec5ea0918254d03b540ef8b8a64d53
• https://git.kernel.org/stable/c/1e950b9a841bc96e98ee25680d5c7aa305120be1
• https://git.kernel.org/stable/c/28ea268d95e57cdf6394a058f0d854206d478772
• https://git.kernel.org/stable/c/f1fe40120de6ad4ffa8299fde035a5feba10d4fb
• https://git.kernel.org/stable/c/fc3442247716fc426bbcf62ed65e086e48a6d44f