linux-kernel - [PATCH] aio: Fix io_pgetevents() struct __compat_aio

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Message-Id: <20190821033820.14155-1-guillem@hadrons.org>
Date:   Wed, 21 Aug 2019 05:38:20 +0200
From:   Guillem Jover <guillem@...rons.org>
To:     linux-aio@...ck.org
Cc:     Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        Benjamin LaHaise <bcrl@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] aio: Fix io_pgetevents() struct __compat_aio_sigset layout

This type is used to pass the sigset_t from userland to the kernel,
but it was using the kernel native pointer type for the member
representing the compat userland pointer to the userland sigset_t.

This messes up the layout, and makes the kernel eat up both the
userland pointer and the size members into the kernel pointer, and
then reads garbage into the kernel sigsetsize. Which makes the sigset_t
size consistency check fail, and consequently the syscall always
returns -EINVAL.

This breaks both libaio and strace on 32-bit userland running on 64-bit
kernels. And there are apparently no users in the wild of the current
broken layout (at least according to codesearch.debian.org and a brief
check over github.com search). So it looks safe to fix this directly
in the kernel, instead of either letting userland deal with this
permanently with the additional overhead or trying to make the syscall
infer what layout userland used, even though this is also being worked
around in libaio to temporarily cope with kernels that have not yet
been fixed.

We use a proper compat_uptr_t instead of a compat_sigset_t pointer.

Fixes: 7a074e96 ("aio: implement io_pgetevents")
Signed-off-by: Guillem Jover <guillem@...rons.org>
---
 fs/aio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 01e0fb9ae45a..056f291bc66f 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -2179,7 +2179,7 @@ SYSCALL_DEFINE5(io_getevents_time32, __u32, ctx_id,
 #ifdef CONFIG_COMPAT

 struct __compat_aio_sigset {
-	compat_sigset_t __user	*sigmask;
+	compat_uptr_t		sigmask;
 	compat_size_t		sigsetsize;
 };

@@ -2204,7 +2204,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
 	if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
 		return -EFAULT;

-	ret = set_compat_user_sigmask(ksig.sigmask, ksig.sigsetsize);
+	ret = set_compat_user_sigmask(compat_ptr(ksig.sigmask), ksig.sigsetsize);
 	if (ret)
 		return ret;

@@ -2239,7 +2239,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
 	if (usig && copy_from_user(&ksig, usig, sizeof(ksig)))
 		return -EFAULT;

-	ret = set_compat_user_sigmask(ksig.sigmask, ksig.sigsetsize);
+	ret = set_compat_user_sigmask(compat_ptr(ksig.sigmask), ksig.sigsetsize);
 	if (ret)
 		return ret;

-- 
2.23.0