From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:38075) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghBCR-0006Di-6o for qemu-devel@nongnu.org; Wed, 09 Jan 2019 05:35:11 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ghBCP-0004pp-5c for qemu-devel@nongnu.org; Wed, 09 Jan 2019 05:35:03 -0500 Received: from mail-wr1-f67.google.com ([209.85.221.67]:44669) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ghBCO-0004pP-Vz for qemu-devel@nongnu.org; Wed, 09 Jan 2019 05:35:01 -0500 Received: by mail-wr1-f67.google.com with SMTP id z5so7072071wrt.11 for ; Wed, 09 Jan 2019 02:35:00 -0800 (PST) References: <20190108184900.9654-1-peter.maydell@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <85b11940-88b8-9a8e-aa8c-f3e2a60a3d2c@redhat.com> Date: Wed, 9 Jan 2019 11:34:57 +0100 MIME-Version: 1.0 In-Reply-To: <20190108184900.9654-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [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: Peter Maydell , qemu-devel@nongnu.org Cc: Riku Voipio , Laurent Vivier On 1/8/19 7:49 PM, Peter Maydell wrote: > 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) { And this if() is now more readable, thanks. Reviewed-by: Philippe Mathieu-Daudé > + 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; >