From 11b5d164777c800e1e1d4553e3e8929de92d21c2 Mon Sep 17 00:00:00 2001 From: Guillem Jover Date: Fri, 16 Aug 2019 02:33:46 +0200 Subject: [PATCH libaio 2/3] Fix io_pgetevents() syscall wrapper on 32-bit userland on 64-bit kernels The kernel compat syscall got introduced in the kernel with a broken layout, which requires a pointer to the actual sigset_t variable but with the size of the running kernel, not the size of the compat code. This means that when the wrapper sends the expected 32-bit compat pointer, the kernel reads a 64-bit pointer, eating with it also the sigset_t size member. And then proceeds to fail the comparison of the sigset_t size and returns EINVAL. This really needs to be fixed in the kernel, as there's no apparent user of the broken compat layout (from codesearch.debian.org, nor a quick github.com search). But we have to workaround it in libaio so that we can use kernels that have not yet been fixed. We do that by trying the non-broken layout (that would be used with a 32-bit userland on a 32-bit kernel) to not penalyzed these, and if that fails with -EINVAL we retry with a structure padded to what the kernel expects. Signed-off-by: Guillem Jover --- src/io_pgetevents.c | 38 +++++++++++++++++++++++++++++++------- src/libaio.h | 12 ++++++++++++ 2 files changed, 43 insertions(+), 7 deletions(-) diff --git a/src/io_pgetevents.c b/src/io_pgetevents.c index e6b0614..b2515f2 100644 --- a/src/io_pgetevents.c +++ b/src/io_pgetevents.c @@ -33,17 +33,41 @@ int io_pgetevents(io_context_t ctx, long min_nr, long nr, struct io_event *events, struct timespec *timeout, sigset_t *sigmask) { - struct { - unsigned long ss; - unsigned long ss_len; - } data; + struct io_sigset aio_sigset; +#ifndef __LP64__ + struct io_sigset_compat aio_sigset_compat = { 0 }; +#endif + int ret; if (aio_ring_is_empty(ctx, timeout)) return 0; - data.ss = (unsigned long)sigmask; - data.ss_len = _NSIG / 8; - return __io_pgetevents(ctx, min_nr, nr, events, timeout, &data); + aio_sigset.ss = (unsigned long)sigmask; + aio_sigset.ss_len = _NSIG / 8; + ret = __io_pgetevents(ctx, min_nr, nr, events, timeout, &aio_sigset); + +#ifndef __LP64__ + /* + * The compat kernel syscall got introduced with an broken layout for + * its sigset argument, expecting it to contain a pointer for the + * non-compat pointer size. + * + * To cope with this on unfixed kernels, in case we are built as a + * 32-bit library (which could run on a kernel with compat code) and + * when the syscall returns EINVAL due to the kernel not finding the + * sigset size member when unpacking the structure, we retry with + * the fixed up compat layout, which requires the padding to be + * zero-filled, otherwise the 64-bit pointer will contain garbage. + */ + if (ret != -EINVAL) + return ret; + + aio_sigset_compat.ss = (unsigned long)sigmask; + aio_sigset_compat.ss_len = _NSIG / 8; + ret = __io_pgetevents(ctx, min_nr, nr, events, timeout, &aio_sigset_compat); +#endif + + return ret; } #else int io_pgetevents(io_context_t ctx, long min_nr, long nr, diff --git a/src/libaio.h b/src/libaio.h index 8b33382..238744b 100644 --- a/src/libaio.h +++ b/src/libaio.h @@ -144,6 +144,18 @@ struct io_event { PADDEDul(res2, __pad4); }; +struct io_sigset { + unsigned long ss; + unsigned long ss_len; +}; + +#ifndef __LP64__ +struct io_sigset_compat { + PADDEDptr(unsigned long ss, __ss_pad); + unsigned long ss_len; +}; +#endif + #undef PADDED #undef PADDEDptr #undef PADDEDul -- 2.23.0