New submission from William Meehan <[email protected]>:
The existing implementation of PyOS_mystricmp increments both pointers as long
as the first string hasn't reached the end yet. If the second string ends
first, then we increment past the null byte. If there is a difference in the
middle of the two strings, then the result actually compares the following pair
of letters.
e.g.
PyOS_mystricmp("a", "\0") => 0 (should be positive)
PyOS_mystricmp("foo", "fro") => 0 (should be negative)
Similarly, PyOS_mystrnicmp increments the pointers in a condition before
breaking out of the loop. It's possible to increment the first pointer without
incrementing the second, and the result is the character past the null byte.
e.g.
PyOS_mystrnicmp("\0a", "\0b", 2) => 97 (should be negative)
----------
components: C API
messages: 375203
nosy: wmeehan
priority: normal
severity: normal
status: open
title: PyOS_mystricmp advances pointers too far
type: behavior
versions: Python 3.10, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python
3.9
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Python tracker <[email protected]>
<https://bugs.python.org/issue41524>
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