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Prevent panic on fuzzer provided string (#14405) (#14409)

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* Prevent panic on fuzzer provided string

The fuzzer has found that providing a <body> tag with an attribute to
PostProcess causes a panic. This PR removes any rendered html or body
tags from the output.

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Placate lint

* placate lint again

Signed-off-by: Andrew Thornton <art27@cantab.net>

* minor cleanup

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>
This commit is contained in:
6543
2021-01-20 19:47:30 +01:00
committed by GitHub
parent 0c3f95034a
commit fb274ec54b
2 changed files with 53 additions and 10 deletions
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38
modules/markup/html.go
View File

@ -298,9 +298,6 @@ func RenderEmoji(
return ctx.postProcess(rawHTML)
}
var byteBodyTag = []byte("<body>")
var byteBodyTagClosing = []byte("</body>")
func (ctx *postProcessCtx) postProcess(rawHTML []byte) ([]byte, error) {
if ctx.procs == nil {
ctx.procs = defaultProcessors
@ -308,9 +305,9 @@ func (ctx *postProcessCtx) postProcess(rawHTML []byte) ([]byte, error) {
// give a generous extra 50 bytes
res := make([]byte, 0, len(rawHTML)+50)
res = append(res, byteBodyTag...)
res = append(res, "<html><body>"...)
res = append(res, rawHTML...)
res = append(res, byteBodyTagClosing...)
res = append(res, "</body></html>"...)
// parse the HTML
nodes, err := html.ParseFragment(bytes.NewReader(res), nil)
@ -322,6 +319,31 @@ func (ctx *postProcessCtx) postProcess(rawHTML []byte) ([]byte, error) {
ctx.visitNode(node, true)
}
newNodes := make([]*html.Node, 0, len(nodes))
for _, node := range nodes {
if node.Data == "html" {
node = node.FirstChild
for node != nil && node.Data != "body" {
node = node.NextSibling
}
}
if node == nil {
continue
}
if node.Data == "body" {
child := node.FirstChild
for child != nil {
newNodes = append(newNodes, child)
child = child.NextSibling
}
} else {
newNodes = append(newNodes, node)
}
}
nodes = newNodes
// Create buffer in which the data will be placed again. We know that the
// length will be at least that of res; to spare a few alloc+copy, we
// reuse res, resetting its length to 0.
@ -334,12 +356,8 @@ func (ctx *postProcessCtx) postProcess(rawHTML []byte) ([]byte, error) {
}
}
// remove initial parts - because Render creates a whole HTML page.
res = buf.Bytes()
res = res[bytes.Index(res, byteBodyTag)+len(byteBodyTag) : bytes.LastIndex(res, byteBodyTagClosing)]
// Everything done successfully, return parsed data.
return res, nil
return buf.Bytes(), nil
}
func (ctx *postProcessCtx) visitNode(node *html.Node, visitText bool) {