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From ba42ebb863ab7d40adc79298422ed9596df8f73a Mon Sep 17 00:00:00 2001
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From: Li Qiang <liqiang6-s@360.cn>
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Date: Mon, 17 Oct 2016 14:13:58 +0200
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Subject: [PATCH] 9pfs: allocate space for guest originated empty strings
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If a guest sends an empty string paramater to any 9P operation, the current
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code unmarshals it into a V9fsString equal to { .size = 0, .data = NULL }.
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This is unfortunate because it can cause NULL pointer dereference to happen
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at various locations in the 9pfs code. And we don't want to check str->data
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everywhere we pass it to strcmp() or any other function which expects a
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dereferenceable pointer.
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This patch enforces the allocation of genuine C empty strings instead, so
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callers don't have to bother.
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Out of all v9fs_iov_vunmarshal() users, only v9fs_xattrwalk() checks if
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the returned string is empty. It now uses v9fs_string_size() since
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name.data cannot be NULL anymore.
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Signed-off-by: Li Qiang <liqiang6-s@360.cn>
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[groug, rewritten title and changelog,
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fix empty string check in v9fs_xattrwalk()]
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Signed-off-by: Greg Kurz <groug@kaod.org>
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---
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fsdev/9p-iov-marshal.c | 2 +-
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hw/9pfs/9p.c | 2 +-
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2 files changed, 2 insertions(+), 2 deletions(-)
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diff --git a/fsdev/virtio-9p-marshal.c b/fsdev/9p-iov-marshal.c
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index 663cad5..1d16f8d 100644
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--- a/fsdev/virtio-9p-marshal.c
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+++ b/fsdev/virtio-9p-marshal.c
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@@ -125,7 +125,7 @@ ssize_t v9fs_iov_vunmarshal(struct iovec *out_sg, int out_num, size_t offset,
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str->data = g_malloc(str->size + 1);
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copied = v9fs_unpack(str->data, out_sg, out_num, offset,
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str->size);
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- if (copied > 0) {
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+ if (copied >= 0) {
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str->data[str->size] = 0;
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} else {
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v9fs_string_free(str);
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diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/9p.c
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index 119ee58..39a7e1d 100644
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--- a/hw/9pfs/virtio-9p.c
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+++ b/hw/9pfs/virtio-9p.c
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@@ -3174,7 +3174,7 @@ static void v9fs_xattrwalk(void *opaque)
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goto out;
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}
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v9fs_path_copy(&xattr_fidp->path, &file_fidp->path);
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- if (name.data == NULL) {
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+ if (!v9fs_string_size(&name)) {
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/*
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* listxattr request. Get the size first
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*/
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--
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1.7.0.4
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