CVE-2026-53402

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

fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()

When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the err_out label to roll back the console state. However, the current rollback logic forgets to restore the hi_font state, leading to a severe state machine corruption.

Earlier in the function, set_vc_hi_font() might be called to change vc->vc_hi_font_mask and mutate the screen buffer. If vc_resize() subsequently fails, the err_out path restores vc_font.charcount but entirely skips rolling back the vc_hi_font_mask and the screen buffer.

This mismatch leaves the terminal in a desynchronized state. Because vc_hi_font_mask remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., fbcon_putcs()) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure.

Fix this by adding the missing rollback logic for the hi_font mask and screen buffer in the error path.

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/076b1aa65f77a49bce5a48a4a55a397cfcafa2b8
• https://git.kernel.org/stable/c/3618a4c5b2591cfa83efe74f5b18c2d02b35c3f5
• https://git.kernel.org/stable/c/39815715cbcfabb16fc8c5f4a23deeda20f5df62
• https://git.kernel.org/stable/c/8fdc8c2057eea08d40ce2c8eed41ff9e451c65c2
• https://git.kernel.org/stable/c/a7a526fbc847f07ad3a503c7382189be5ab68574
• https://git.kernel.org/stable/c/ac562193c36696513ae196171892e9338475c4bc
• https://git.kernel.org/stable/c/b5bb2c696e140c399cb874def2feedf61dee27d6
• https://git.kernel.org/stable/c/cb016bcb40c81e7b19c4ae6143babb366dae8e20