From: Seth Jenkins <sethjenkins@google.com>
Date: Tue, 31 Jan 2023 17:25:55 +0000 (-0500)
Subject: aio: fix mremap after fork null-deref
X-Git-Tag: v5.10.169~42
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c261f798f7baa8080cf0214081d43d5f86bb073f;p=thirdparty%2Fkernel%2Fstable.git

aio: fix mremap after fork null-deref

commit 81e9d6f8647650a7bead74c5f926e29970e834d1 upstream.

Commit e4a0d3e720e7 ("aio: Make it possible to remap aio ring") introduced
a null-deref if mremap is called on an old aio mapping after fork as
mm->ioctx_table will be set to NULL.

[jmoyer@redhat.com: fix 80 column issue]
Link: https://lkml.kernel.org/r/x49sffq4nvg.fsf@segfault.boston.devel.redhat.com
Fixes: e4a0d3e720e7 ("aio: Make it possible to remap aio ring")
Signed-off-by: Seth Jenkins <sethjenkins@google.com>
Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Jann Horn <jannh@google.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/fs/aio.c b/fs/aio.c
index 2a9dfa58ec3ab..5934ea84b4993 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -335,6 +335,9 @@ static int aio_ring_mremap(struct vm_area_struct *vma)
 	spin_lock(&mm->ioctx_lock);
 	rcu_read_lock();
 	table = rcu_dereference(mm->ioctx_table);
+	if (!table)
+		goto out_unlock;
+
 	for (i = 0; i < table->nr; i++) {
 		struct kioctx *ctx;
 
@@ -348,6 +351,7 @@ static int aio_ring_mremap(struct vm_area_struct *vma)
 		}
 	}
 
+out_unlock:
 	rcu_read_unlock();
 	spin_unlock(&mm->ioctx_lock);
 	return res;