Fix undefined behaviour in unpack() #10943
Closed
+20
−8
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
atoi()'s return value is actually undefined when an underflow or overflow occurs. For example on 32-bit on my system the overflow test which inputs "h2147483648" results in repetitions==2147483647 and on 64-bit this gives repetitions==-2147483648. The reason the test works on 32-bit is because there's a second undefined behaviour problem: in case 'h' when repetitions==2147483647, we add 1 and divide by 2. This is signed-wrap undefined behaviour and accidentally triggers the overflow check like we wanted to. Avoid all this trouble and use strtol with explicit error checking. This also fixes a semantic bug where repetitions==INT_MAX would result in the overflow check to trigger, even though there is no overflow.
Girgias
reviewed
Mar 26, 2023
Girgias
approved these changes
Mar 28, 2023
|
This was for unpack(), but looks like the pack() function has the same problem. I'll try to look at it this week sometime. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
atoi()'s return value is actually undefined when an underflow or overflow occurs. For example on 32-bit on my system the overflow test which inputs "h2147483648" results in repetitions==2147483647 and on 64-bit this gives repetitions==-2147483648. The reason the test works on 32-bit is because there's a second undefined behaviour problem: in case 'h' when repetitions==2147483647, we add 1 and divide by 2. This is signed-wrap undefined behaviour and accidentally triggers the overflow check like we wanted to.
Avoid all this trouble and use strtol with explicit error checking.
This also fixes a semantic bug where repetitions==INT_MAX would result in the overflow check to trigger, even though there is no overflow.