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linux-user: make pwrite64/pread64(fd, NULL, 0, offset) return 0 

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 58cfa6c2e6
for the write syscall, and long before that in 38d840e679
for the read syscall.

Fixes: https://bugs.launchpad.net/qemu/+bug/1810433

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190108184900.9654-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
(cherry picked from commit 2bd3f8998e)
*drop functional dep. on 2852aafd9d
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
stable-3.0
Peter Maydell 2019-01-08 18:49:00 +00:00 committed by Michael Roth
parent 89d2237683
commit 422bf25df1
1 changed files with 18 additions and 4 deletions
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22
linux-user/syscall.c
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@ -10910,8 +10910,15 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
arg4 = arg5;
arg5 = arg6;
}
if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
goto 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) {
goto efault;
}
}
ret = get_errno(pread64(arg1, p, arg3, target_offset64(arg4, arg5)));
unlock_user(p, arg2, ret);
break;
@ -10920,8 +10927,15 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
arg4 = arg5;
arg5 = arg6;
}
if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))
goto 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) {
goto efault;
}
}
ret = get_errno(pwrite64(arg1, p, arg3, target_offset64(arg4, arg5)));
unlock_user(p, arg2, 0);
break;