CodeQL documentation

Shift out of range

ID: go/shift-out-of-range
Kind: problem
Severity: warning
Precision: very-high
Tags:
   - correctness
   - external/cwe/cwe-197
Query suites:
   - go-security-and-quality.qls

Click to see the query in the CodeQL repository

Shifting an integer value by more than the number of bits in its type always results in -1 for right-shifts of negative values and 0 for other shifts. Hence, such a shift expression is either redundant or indicates a logic mistake.

Recommendation

Examine the length check to see whether it is redundant and can be removed, or a mistake that should be fixed.

Example

The following code snippet attempts to compute the value 240 (1099511627776). However, since the left operand base is of type int32 (32 bits), the shift operation overflows, yielding zero.

package main

func shift(base int32) int32 {
	return base << 40
}

var x1 = shift(1)

To prevent this, the type of base should be changed to int64:

package main

func shiftGood(base int64) int64 {
	return base << 40
}

var x2 = shiftGood(1)

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