If the specified needle crosses a page-boundary, the s390-z15 ifunc variant of strstr truncates the needle which results in invalid results. Example: needle = "Hello" <page-boundary> "World" really used needle = "Hello" haystack = "abc HelloBug def" result = "HelloBug def" This only happens if the needle before page-boundary contains 9 or less characters. The s390-z15 ifunc variant of strstr was introduces in glibc 2.30.
The master branch has been updated by Stefan Liebler <stli@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=bfdb731438206b0f70fe7afa890681155c30b419 commit bfdb731438206b0f70fe7afa890681155c30b419 Author: Stefan Liebler <stli@linux.ibm.com> Date: Wed Nov 27 12:35:40 2019 +0100 S390: Fix handling of needles crossing a page in strstr z15 ifunc-variant. [BZ #25226] If the specified needle crosses a page-boundary, the s390-z15 ifunc variant of strstr truncates the needle which results in invalid results. This is fixed by loading the needle beyond the page boundary to v18 instead of v16. The bug is sometimes observable in test-strstr.c in check1 and check2 as the haystack and needle is stored on stack. Thus the needle can be on a page boundary. check2 is now extended to test haystack / needles located on stack, at end of page and on two pages. This bug was introduced with commit 6f47401bd5fc71209219779a0426170a9a7395b0 ("S390: Add arch13 strstr ifunc variant.") and is already released in glibc 2.30.
The release/2.30/master branch has been updated by Stefan Liebler <stli@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f4419b0d0181da28f18cba40068f2e75300f5020 commit f4419b0d0181da28f18cba40068f2e75300f5020 Author: Stefan Liebler <stli@linux.ibm.com> Date: Wed Nov 27 12:35:40 2019 +0100 S390: Fix handling of needles crossing a page in strstr z15 ifunc-variant. [BZ #25226] If the specified needle crosses a page-boundary, the s390-z15 ifunc variant of strstr truncates the needle which results in invalid results. This is fixed by loading the needle beyond the page boundary to v18 instead of v16. The bug is sometimes observable in test-strstr.c in check1 and check2 as the haystack and needle is stored on stack. Thus the needle can be on a page boundary. check2 is now extended to test haystack / needles located on stack, at end of page and on two pages. This bug was introduced with commit 6f47401bd5fc71209219779a0426170a9a7395b0 ("S390: Add arch13 strstr ifunc variant.") and is already released in glibc 2.30. (cherry picked from commit bfdb731438206b0f70fe7afa890681155c30b419)
Resolved upstream and backported to glibc 2.30 release branch. See comments 1 and 2.