Skip to content

linux: fix readlinkat guest copy length handling #67

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
fwsGonzo merged 1 commit into from
Apr 4, 2026
+12 −7
Merged

linux: fix readlinkat guest copy length handling #67

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 12 additions & 7 deletions lib/tinykvm/linux/system_calls.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
#include "threads.hpp"
#include <cstring>
#include <fcntl.h>
#include <limits.h>
#include <netinet/in.h>
#include <sched.h>
#include <signal.h>
Expand Down Expand Up @@ -2892,9 +2893,10 @@ void Machine::setup_linux_system_calls(bool unsafe_syscalls)
path = cpu.machine().memcstring(vpath, PATH_MAX);
// Check if the path is a symlink
if (cpu.machine().fds().resolve_symlink(path)) {
// Copy the resolved path to the guest
cpu.machine().copy_to_guest(g_buffer, path.c_str(), path.size());
regs.rax = path.size();
// Copy the resolved path to the guest, respecting guest buffer size.
const size_t copied = std::min<size_t>(path.size(), g_size);
cpu.machine().copy_to_guest(g_buffer, path.c_str(), copied);
regs.rax = copied;
}
else if (UNLIKELY(!cpu.machine().fds().is_readable_path(path))) {
// Pretend the path is not a link
Expand All @@ -2904,10 +2906,13 @@ void Machine::setup_linux_system_calls(bool unsafe_syscalls)
// Translate from vfd when fd != AT_FDCWD
if (vfd != AT_FDCWD)
fd = cpu.machine().fds().translate(vfd);
// Path is in allow-list
regs.rax = readlinkat(fd, path.c_str(), (char *)g_buffer, g_size);
if (regs.rax > 0) {
cpu.machine().copy_to_guest(g_buffer, path.c_str(), regs.rax);
// Read link target into host buffer, then copy to guest memory.
char host_buffer[PATH_MAX];
const size_t host_size = std::min<size_t>(g_size, sizeof(host_buffer));
const ssize_t bytes = readlinkat(fd, path.c_str(), host_buffer, host_size);
if (bytes >= 0) {
cpu.machine().copy_to_guest(g_buffer, host_buffer, size_t(bytes));
regs.rax = bytes;
} else {
regs.rax = -errno;
}
Expand Down