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[2a02:1811:cc83:eef0:f2b6:6987:9238:41ca]) by smtp.gmail.com with ESMTPSA id o14-20020a170906774e00b006d5b915f27dsm7351657ejn.169.2022.04.27.15.46.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 27 Apr 2022 15:46:19 -0700 (PDT) From: Niels Dossche To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mina Almasry , Niels Dossche Subject: [PATCH 0/2] mm: mremap: fix sign for EFAULT error return value Date: Thu, 28 Apr 2022 00:44:37 +0200 Message-Id: <20220427224439.23828-1-dossche.niels@gmail.com> X-Mailer: git-send-email 2.35.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: nzjkx34wm9z83ycmidt9h4nfygf7g5ck X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 26DA012005B Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Gndc1RCG; spf=pass (imf29.hostedemail.com: domain of dossche.niels@gmail.com designates 209.85.208.52 as permitted sender) smtp.mailfrom=dossche.niels@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-HE-Tag: 1651099577-222810 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The mremap syscall is supposed to return a pointer to the new virtual memory area on success, and a negative value of the error code in case of failure. Currently, EFAULT is returned when the VMA is not found, instead of -EFAULT. The users of this syscall will therefore believe the syscall succeeded in case the VMA didn't exist, as it returns a pointer to address 0xe (0xe being the value of EFAULT). This can easily be reproduced by the following C program. I expected mremap to fail, but it does not. If the bug is present, it will print 0xe, otherwise the mremap will fail. The patchset contains two patches: one that fixes the error, and one that adds a small test case. #define _GNU_SOURCE #include #include int main() { // Get pointer that's definitely not mapped void* ptr = mmap(NULL, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (ptr == MAP_FAILED) { perror("mmap"); return 1; } int err = munmap(ptr, 4096); if (err < 0) { perror("munmap"); return 1; } // Remap unexisting VMA ptr = mremap(ptr, 4096, 4096, 0); if (ptr == MAP_FAILED) { perror("mremap"); return 1; } printf("%p\n", ptr); return 0; } Niels Dossche (2): mm: mremap: fix sign for EFAULT error return value selftest/vm: test that mremap fails on non-existent vma mm/mremap.c | 2 +- tools/testing/selftests/vm/hugepage-mremap.c | 6 ++++++ 2 files changed, 7 insertions(+), 1 deletion(-) -- 2.35.2