This commit adds support for the `openat2()` syscall in the `linux-user` userspace emulator.
It is implemented by extracting a new helper `maybe_do_fake_open()` out of the exiting `do_guest_openat()` and share that with the new `do_guest_openat2()`. Unfortunatly we cannot just make do_guest_openat2() a superset of do_guest_openat() because the openat2() syscall is stricter with the argument checking and will return an error for invalid flags or mode combinations (which open()/openat() will ignore). Note that in this commit using openat2() for a "faked" file in /proc will ignore the "resolve" flags. This is not great but it seems similar to the exiting behavior when openat() is called with a dirfd to "/proc". Here too the fake file lookup may not catch the special file because "realpath()" is used to determine if the path is in /proc. Alternatively to ignoring we could simply fail with `-TARGET_ENOSYS` (or similar) if `resolve` flags are passed and we found something that looks like a file in /proc that needs faking. Signed-off-by: Michael Vogt <mv...@redhat.com> Buglink: https://github.com/osbuild/bootc-image-builder/issues/619 --- linux-user/qemu.h | 4 +++ linux-user/syscall.c | 73 ++++++++++++++++++++++++++++++++++++--- linux-user/syscall_defs.h | 7 ++++ meson.build | 1 + 4 files changed, 81 insertions(+), 4 deletions(-) diff --git a/linux-user/qemu.h b/linux-user/qemu.h index 2e90a97175..47b6d7da88 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -164,6 +164,10 @@ struct TaskState { abi_long do_brk(abi_ulong new_brk); int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int flags, mode_t mode, bool safe); +#ifdef HAVE_OPENAT2_H +int do_guest_openat2(CPUArchState *cpu_env, int dirfd, const char *pathname, + struct target_open_how *how, bool safe); +#endif ssize_t do_guest_readlink(const char *pathname, char *buf, size_t bufsiz); /* user access */ diff --git a/linux-user/syscall.c b/linux-user/syscall.c index 9d5415674d..f3a47bbfc0 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -85,6 +85,12 @@ #include <sys/kcov.h> #endif +#ifdef HAVE_OPENAT2_H +#include <linux/openat2.h> +/* glibc has no header for SYS_openat2 so we need to get it via syscall.h */ +#include <sys/syscall.h> +#endif + #define termios host_termios #define winsize host_winsize #define termio host_termio @@ -653,6 +659,10 @@ safe_syscall3(ssize_t, read, int, fd, void *, buff, size_t, count) safe_syscall3(ssize_t, write, int, fd, const void *, buff, size_t, count) safe_syscall4(int, openat, int, dirfd, const char *, pathname, \ int, flags, mode_t, mode) +#ifdef HAVE_OPENAT2_H +safe_syscall4(int, openat2, int, dirfd, const char *, pathname, \ + const struct open_how *, how, size_t, size); +#endif #if defined(TARGET_NR_wait4) || defined(TARGET_NR_waitpid) safe_syscall4(pid_t, wait4, pid_t, pid, int *, status, int, options, \ struct rusage *, rusage) @@ -8334,8 +8344,9 @@ static int open_net_route(CPUArchState *cpu_env, int fd) } #endif -int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *fname, - int flags, mode_t mode, bool safe) +static int maybe_do_fake_open(CPUArchState *cpu_env, int dirfd, + const char *fname, int flags, mode_t mode, + bool safe) { g_autofree char *proc_name = NULL; const char *pathname; @@ -8418,13 +8429,48 @@ int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *fname, return fd; } + return -1; +} + +int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *fname, + int flags, mode_t mode, bool safe) +{ + int fd = maybe_do_fake_open(cpu_env, dirfd, fname, flags, mode, safe); + if (fd >= 0) + return fd; + if (safe) { - return safe_openat(dirfd, path(pathname), flags, mode); + return safe_openat(dirfd, path(fname), flags, mode); } else { - return openat(dirfd, path(pathname), flags, mode); + return openat(dirfd, path(fname), flags, mode); } } +#ifdef HAVE_OPENAT2_H +int do_guest_openat2(CPUArchState *cpu_env, int dirfd, const char *fname, + struct target_open_how *how, bool safe) +{ + /* + * Ideally we would pass "how->resolve" flags into this helper too but + * the lookup for files that need faking is based on "realpath()" so + * neither a dirfd for "proc" nor restrictions via "resolve" flags can + * be honored right now. + */ + int fd = maybe_do_fake_open(cpu_env, dirfd, fname, how->flags, how->mode, + safe); + if (fd >= 0) + return fd; + + if (safe) { + return safe_openat2(dirfd, fname, (struct open_how *)how, + sizeof(struct target_open_how)); + } else { + return syscall(SYS_openat2, dirfd, fname, (struct open_hosw *)how, + sizeof(struct target_open_how)); + } +} +#endif + ssize_t do_guest_readlink(const char *pathname, char *buf, size_t bufsiz) { ssize_t ret; @@ -9197,6 +9243,25 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, fd_trans_unregister(ret); unlock_user(p, arg2, 0); return ret; +#if defined(TARGET_NR_openat2) && defined(HAVE_OPENAT2_H) + case TARGET_NR_openat2: + { + struct target_open_how how, *target_how; + if (!(p = lock_user_string(arg2))) + return -TARGET_EFAULT; + if (!(lock_user_struct(VERIFY_READ, target_how, arg3, 1))) + return -TARGET_EFAULT; + how.flags = target_to_host_bitmask(target_how->flags, + fcntl_flags_tbl); + how.mode = tswap64(target_how->mode); + how.resolve = tswap64(target_how->resolve); + ret = get_errno(do_guest_openat2(cpu_env, arg1, p, &how, true)); + fd_trans_unregister(ret); + unlock_user_struct(target_how, arg3, 0); + unlock_user(p, arg2, 0); + return ret; + } +#endif #if defined(TARGET_NR_name_to_handle_at) && defined(CONFIG_OPEN_BY_HANDLE) case TARGET_NR_name_to_handle_at: ret = do_name_to_handle_at(arg1, arg2, arg3, arg4, arg5); diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h index a00b617cae..2ae694261c 100644 --- a/linux-user/syscall_defs.h +++ b/linux-user/syscall_defs.h @@ -2754,4 +2754,11 @@ struct target_sched_param { abi_int sched_priority; }; +/* from kernel's include/uapi/linux/openat2.h */ +struct target_open_how { + __u64 flags; + __u64 mode; + __u64 resolve; +}; + #endif diff --git a/meson.build b/meson.build index fbda17c987..220ccbcbe6 100644 --- a/meson.build +++ b/meson.build @@ -2465,6 +2465,7 @@ config_host_data.set('CONFIG_LINUX_MAGIC_H', cc.has_header('linux/magic.h')) config_host_data.set('CONFIG_VALGRIND_H', cc.has_header('valgrind/valgrind.h')) config_host_data.set('HAVE_BTRFS_H', cc.has_header('linux/btrfs.h')) config_host_data.set('HAVE_DRM_H', cc.has_header('libdrm/drm.h')) +config_host_data.set('HAVE_OPENAT2_H', cc.has_header('linux/openat2.h')) config_host_data.set('HAVE_PTY_H', cc.has_header('pty.h')) config_host_data.set('HAVE_SYS_DISK_H', cc.has_header('sys/disk.h')) config_host_data.set('HAVE_SYS_IOCCOM_H', cc.has_header('sys/ioccom.h')) -- 2.45.2
