Upon failure, a libseccomp API returns actual errno value very rarely. Fortunately, after its commit 34bf78ab (contained in 2.5.0 release), the SCMP_FLTATR_API_SYSRAWRC attribute can be set which makes subsequent APIs return true errno on failure.
This is especially critical when seccomp_load() fails, because generic -ECANCELED says nothing. Signed-off-by: Michal Privoznik <mpriv...@redhat.com> Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org> --- v2 of: https://lists.gnu.org/archive/html/qemu-devel/2022-10/msg04509.html diff to v1: - added comment when setting SYSRAWRC attribute per Philippe's suggestion meson.build | 9 +++++++++ softmmu/qemu-seccomp.c | 13 +++++++++++++ 2 files changed, 22 insertions(+) diff --git a/meson.build b/meson.build index b686dfef75..5f114c89d9 100644 --- a/meson.build +++ b/meson.build @@ -636,10 +636,16 @@ if vmnet.found() and not cc.has_header_symbol('vmnet/vmnet.h', endif seccomp = not_found +seccomp_has_sysrawrc = false if not get_option('seccomp').auto() or have_system or have_tools seccomp = dependency('libseccomp', version: '>=2.3.0', required: get_option('seccomp'), method: 'pkg-config', kwargs: static_kwargs) + if seccomp.found() + seccomp_has_sysrawrc = cc.has_header_symbol('seccomp.h', + 'SCMP_FLTATR_API_SYSRAWRC', + dependencies: seccomp) + endif endif libcap_ng = not_found @@ -1849,6 +1855,9 @@ config_host_data.set('CONFIG_RDMA', rdma.found()) config_host_data.set('CONFIG_SDL', sdl.found()) config_host_data.set('CONFIG_SDL_IMAGE', sdl_image.found()) config_host_data.set('CONFIG_SECCOMP', seccomp.found()) +if seccomp.found() + config_host_data.set('CONFIG_SECCOMP_SYSRAWRC', seccomp_has_sysrawrc) +endif config_host_data.set('CONFIG_SNAPPY', snappy.found()) config_host_data.set('CONFIG_TPM', have_tpm) config_host_data.set('CONFIG_USB_LIBUSB', libusb.found()) diff --git a/softmmu/qemu-seccomp.c b/softmmu/qemu-seccomp.c index deaf8a4ef5..d66a2a1226 100644 --- a/softmmu/qemu-seccomp.c +++ b/softmmu/qemu-seccomp.c @@ -312,6 +312,19 @@ static int seccomp_start(uint32_t seccomp_opts, Error **errp) goto seccomp_return; } +#if defined(CONFIG_SECCOMP_SYSRAWRC) + /* + * This must be the first seccomp_attr_set() call to have full + * error propagation from subsequent seccomp APIs. + */ + rc = seccomp_attr_set(ctx, SCMP_FLTATR_API_SYSRAWRC, 1); + if (rc != 0) { + error_setg_errno(errp, -rc, + "failed to set seccomp rawrc attribute"); + goto seccomp_return; + } +#endif + rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1); if (rc != 0) { error_setg_errno(errp, -rc, -- 2.37.4
