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 <peter.mayd...@linaro.org> --- 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
