http2: Safer invocation of populate_binsettings #12101
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populate_binsettings now returns a negative value on error, instead of a huge positive value. Both places which call this function have been updated to handle this change in its contract. The way populate_binsettings had been used prior to this change the huge positive values -- due to signed->unsigned conversion of the potentially negative result of nghttp2_pack_settings_payload which returns negative values on error -- are not possible. But only because http2.c currently always provides a large enough output buffer and provides H2 SETTINGS IVs which pass the verification logic inside nghttp2. If the verification logic were to change or if http2.c started passing in more IVs without increasing the output buffer size, the overflow could become reachable, and libcurl/curl might start leaking memory contents to servers/proxies...
klyubin
commented
Oct 12, 2023
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| binlen = populate_binsettings(binsettings, data); | ||
| if(binlen <= 0) { |
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The check is <= 0 instead of < 0 to be consistent with the pre-existing such check in Curl_http2_request_upgrade (below)
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Thanks! |
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populate_binsettings now returns a negative value on error, instead of a huge positive value. Both places which call this function have been updated to handle this change in its contract.
The way populate_binsettings had been used prior to this change the huge positive values -- due to signed->unsigned conversion of the potentially negative result of
nghttp2_pack_settings_payload which returns negative values on error -- are not possible. But only because http2.c currently always provides a large enough output buffer and provides H2 SETTINGS IVs which pass the verification logic inside nghttp2. If the verification logic were to change or if http2.c started passing in more IVs without increasing the output buffer size, the overflow could become reachable, and libcurl/curl might start leaking memory contents to servers/proxies...