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To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>, Kyle Huey <me@kylehuey.com>
From:   Jens Axboe <axboe@kernel.dk>
Subject: [PATCH] Fix compat regression in process_vm_rw()
Message-ID: <f69575e0-5170-2d51-8d74-8b3453723aa3@kernel.dk>
Date:   Mon, 26 Oct 2020 18:03:18 -0600
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The removal of compat_process_vm_{readv,writev} didn't change
process_vm_rw(), which always assumes it's not doing a compat syscall.
Instead of passing in 'false' unconditionally for 'compat', make it
conditional on in_compat_syscall().

Fixes: c3973b401ef2 ("mm: remove compat_process_vm_{readv,writev}")
Reported-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index fd12da80b6f2..05676722d9cd 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -273,7 +273,8 @@ static ssize_t process_vm_rw(pid_t pid,
 		return rc;
 	if (!iov_iter_count(&iter))
 		goto free_iov_l;
-	iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r, false);
+	iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
+				in_compat_syscall());
 	if (IS_ERR(iov_r)) {
 		rc = PTR_ERR(iov_r);
 		goto free_iov_l;

-- 
Jens Axboe