From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:57813) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ggwR0-0001ZG-E1 for qemu-devel@nongnu.org; Tue, 08 Jan 2019 13:49:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ggwQz-00051z-Dk for qemu-devel@nongnu.org; Tue, 08 Jan 2019 13:49:06 -0500 Received: from mail-wm1-x344.google.com ([2a00:1450:4864:20::344]:52331) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ggwQz-0004wF-3I for qemu-devel@nongnu.org; Tue, 08 Jan 2019 13:49:05 -0500 Received: by mail-wm1-x344.google.com with SMTP id m1so5168344wml.2 for ; Tue, 08 Jan 2019 10:49:03 -0800 (PST) From: Peter Maydell Date: Tue, 8 Jan 2019 18:49:00 +0000 Message-Id: <20190108184900.9654-1-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH] linux-user: make pwrite64/pread64(fd, NULL, 0, offset) return 0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Riku Voipio , Laurent Vivier Linux returns success if pwrite64() or pread64() are called with a zero length NULL buffer, but QEMU was returning -TARGET_EFAULT. This is the same bug that we fixed in commit 58cfa6c2e6eb51b23cc9 for the write syscall, and long before that in 38d840e6790c29f59 for the read syscall. Fixes: https://bugs.launchpad.net/qemu/+bug/1810433 Signed-off-by: Peter Maydell --- I chose to fix this by setting p to NULL and falling through to the normal-case codepath rather than having a call to pread/pwrite in the special-case if like 58cfa6c2e6eb5, because here the normal-case is a bit more complicated as it has the target_offset64() call in it. 38d840e6790c29f59 has "just return 0" for the NULL buffer case, but we can't do that here as that would not get the "negative offset should return -EINVAL" case write. --- linux-user/syscall.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 280137da8c2..b13a170e52e 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -9677,8 +9677,15 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1, arg4 = arg5; arg5 = arg6; } - if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0))) - return -TARGET_EFAULT; + if (arg2 == 0 && arg3 == 0) { + /* Special-case NULL buffer and zero length, which should succeed */ + p = 0; + } else { + p = lock_user(VERIFY_WRITE, arg2, arg3, 0); + if (!p) { + return -TARGET_EFAULT; + } + } ret = get_errno(pread64(arg1, p, arg3, target_offset64(arg4, arg5))); unlock_user(p, arg2, ret); return ret; @@ -9687,8 +9694,15 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1, arg4 = arg5; arg5 = arg6; } - if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1))) - return -TARGET_EFAULT; + if (arg2 == 0 && arg3 == 0) { + /* Special-case NULL buffer and zero length, which should succeed */ + p = 0; + } else { + p = lock_user(VERIFY_READ, arg2, arg3, 1); + if (!p) { + return -TARGET_EFAULT; + } + } ret = get_errno(pwrite64(arg1, p, arg3, target_offset64(arg4, arg5))); unlock_user(p, arg2, 0); return ret; -- 2.20.1