[PATCH kvmtool v2 3/3] kvmtool: 9p: fix overapping snprintf

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GCC 8.2 gives this warning:

virtio/9p.c: In function ‘virtio_p9_create’:
virtio/9p.c:335:21: error: passing argument 1 to restrict-qualified parameter aliases with argument 4 [-Werror=restrict]
  ret = snprintf(dfid->path, size, "%s/%s", dfid->path, name);
                 ~~~~^~~~~~                 ~~~~~~~~~~

Fix it by allocating a temporary string with dfid->path content instead
of overwriting it in-place, which is limited in glibc snprintf with the
__restrict qualifier.

Signed-off-by: Anisse Astier <aastier@xxxxxxxxxx>
---
 virtio/9p.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/virtio/9p.c b/virtio/9p.c
index 6bae403..ac70dbc 100644
--- a/virtio/9p.c
+++ b/virtio/9p.c
@@ -322,6 +322,7 @@ static void virtio_p9_create(struct p9_dev *p9dev,
 	struct p9_qid qid;
 	struct p9_fid *dfid;
 	char full_path[PATH_MAX];
+	char *tmp_path;
 	u32 dfid_val, flags, mode, gid;
 
 	virtio_p9_pdu_readf(pdu, "dsddd", &dfid_val,
@@ -332,7 +333,13 @@ static void virtio_p9_create(struct p9_dev *p9dev,
 		goto err_out;
 
 	size = sizeof(dfid->abs_path) - (dfid->path - dfid->abs_path);
-	ret = snprintf(dfid->path, size, "%s/%s", dfid->path, name);
+
+	tmp_path = strdup(dfid->path);
+	if (!tmp_path)
+		goto err_out;
+
+	ret = snprintf(dfid->path, size, "%s/%s", tmp_path, name);
+	free(tmp_path);
 	if (ret >= (int)size) {
 		errno = ENAMETOOLONG;
 		if (size > 0)
-- 
2.19.1




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