[Bug 3730] New: Integer overflow when adding 6000 and display_number

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=3730

            Bug ID: 3730
           Summary: Integer overflow when adding 6000 and display_number
           Product: Portable OpenSSH
           Version: 9.8p1
          Hardware: Other
                OS: All
            Status: NEW
          Severity: minor
          Priority: P5
         Component: Build system
          Assignee: unassigned-bugs at mindrot.org
          Reporter: suhov.ra at npc-ksb.ru

File:
https://github.com/openssh/openssh-portable/blob/master/channels.c
Line: 5239

There is virtually no chance of integer overflow when adding 6000 to
display_number. The display_number variable is read from a string
containing the value of the DISPLAY environment variable, which
typically points to an X server on the system. The variable is of type
unsigned int, which limits its range of values ​​to 0 to UINT_MAX. In
theory, for overflow to occur, display_number must be large enough that
the sum exceeds the maximum value for unsigned int.

The following check can be added to rule out the possibility of integer
overflow:

if (display_number > UINT_MAX - 6000) {
error("display_number too large, possible integer overflow.");
return -1;
}

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