[REGRESSION] mremap() returns EFAULT instead of EPERM in LTP mseal01

[Jan Polensky <japo@linux.ibm.com>]

Hello,

we've identified a regression in `mremap()` behavior introduced by:

Refrence: 680e69e07d56 ("mm/mremap: check remap conditions earlier")
Linux-Next Tag: next-20250714

The issue is detected by the LTP test `mseal01`:

    ++ '[' '!' -f ltp-bin/runltp ']'
    ++ ltp-bin/testcases/bin/mseal01
    tst_test.c:1999: TINFO: LTP version: 20250530-79-g39072797fa63
    tst_test.c:2002: TINFO: Tested kernel: 6.16.0-rc5-testing-00315-g680e69e07d56 #1 SMP PREEMPT Thu Jul 17 10:59:57 CEST 2025 s390x
    tst_kconfig.c:88: TINFO: Parsing kernel config '/proc/config.gz'
    tst_kconfig.c:676: TINFO: CONFIG_PROVE_LOCKING kernel option detected which might slow the execution
    tst_test.c:1820: TINFO: Overall timeout per run is 0h 02m 00s
    mseal01.c:130: TINFO: Testing mprotect() availability
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    mseal01.c:45: TPASS: mprotect(mem_addr, mem_size, PROT_NONE) : EPERM (1)
    mseal01.c:130: TINFO: Testing pkey_mprotect() availability
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    ../../../../include/lapi/pkey.h:43: TCONF: syscall(385) __NR_pkey_alloc not supported on your arch
    mseal01.c:130: TINFO: Testing madvise() availability
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    mseal01.c:70: TPASS: madvise(mem_addr, mem_size, MADV_DONTNEED) : EPERM (1)
    mseal01.c:130: TINFO: Testing munmap() availability from child
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    mseal01.c:75: TPASS: munmap(mem_addr, mem_size) : EPERM (1)
    mseal01.c:130: TINFO: Testing mremap() address move/resize
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    mseal01.c:88: TFAIL: mremap(mem_addr, mem_size, new_size, MREMAP_MAYMOVE | MREMAP_FIXED, new_addr) expected EPERM: EFAULT (14)
    mseal01.c:130: TINFO: Testing mmap() protection change
    mseal01.c:132: TPASS: sys_mseal(mem_addr + mem_offset, mem_alignment) passed
    mseal01.c:98: TPASS: mmap(mem_addr, mem_size, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0) : EPERM (1)

    Summary:
    passed   10
    failed   1
    broken   0
    skipped  1
    warnings 0

Works before/without the above commit.

LTP-Version:
    20250530

Compiler:
    gcc (GCC) 15.1.1 20250425 (Red Hat 15.1.1-1)
    Copyright (C) 2025 Free Software Foundation, Inc.
    This is free software; see the source for copying conditions.  There is NO
    warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Let me know if further details or a reproducer are needed.

Best regards,
Jan