lib/iov_iter: fix import_iovec_ubuf iovec management

JIRA: https://issues.redhat.com/browse/RHEL-87739

commit f4b7826
Author: Pavel Begunkov <asml.silence@gmail.com>
Date:   Fri Jan 31 14:13:15 2025 +0000

    lib/iov_iter: fix import_iovec_ubuf iovec management

    import_iovec() says that it should always be fine to kfree the iovec
    returned in @iovp regardless of the error code.  __import_iovec_ubuf()
    never reallocates it and thus should clear the pointer even in cases when
    copy_iovec_*() fail.

    Link: https://lkml.kernel.org/r/378ae26923ffc20fd5e41b4360d673bf47b1775b.1738332461.git.asml.silence@gmail.com
    Fixes: 3b2deb0 ("iov_iter: import single vector iovecs as ITER_UBUF")
    Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
    Reviewed-by: Jens Axboe <axboe@kernel.dk>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Christian Brauner <brauner@kernel.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

lib/iov_iter.c

@@ -1839,6 +1839,8 @@ static ssize_t __import_iovec_ubuf(int type, const struct iovec __user *uvec,
 	struct iovec *iov = *iovp;
 	ssize_t ret;
 
+	*iovp = NULL;
+
 	if (compat)
 		ret = copy_compat_iovec_from_user(iov, uvec, 1);
 	else
@@ -1849,7 +1851,6 @@ static ssize_t __import_iovec_ubuf(int type, const struct iovec __user *uvec,
 	ret = import_ubuf(type, iov->iov_base, iov->iov_len, i);
 	if (unlikely(ret))
 		return ret;
-	*iovp = NULL;
 	return i->count;
 }