gnrc_ipv6_ext_frag: fix release on rbuf creation for n-th fragment [backport 2019.10] #12434
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(cherry picked from commit 40f721a)
Adds a test case for when the following conditions cause a crash: - a subsequent fragment is received before the first - the reassembly buffer is currently filled up when another fragment of a different datagram arrives and thus needs to be cached out to make room for the new reassembly (cherry picked from commit 07a6b54)
The IPv6 (extension) headers of the first fragment received are re-used for the reassembled packet, so when receiving a subsequent packet we need to distinguish, if we just want to release the payload or all of the packet after the packet data was added to the reassembly buffer. (cherry picked from commit 095e966)
(cherry picked from commit 18597c4)
miri64
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Area: network
This was referenced Oct 20, 2019
miri64
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backport/2019.10/gnrc_ipv6_ext_frag/fix/n-th-with-full-rbuf
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Backport of #12414
Contribution description
While testing #12375, @kb2ma noticed that in some rare cases, one of the nodes crashes. He informed me offline and I was able to reproduce that. After some more runs, I was able to pinpoint it to the following corner case:
Due to that I added a test case to the unittests of IPv6 reassembly (feee568).
In the end it turned out that when a subsequent fragment is received packet parts that are stored in the reassembly buffer are freed from the packet buffer on reassembly buffer creation. This in turn leads that freed (but still referenced by the reassembly buffer) region to be reused for another packet coming in, e.g. another fragment, that then caches the other reassembly buffer entry out, since the reassembly buffer is full, leading to parts of its data to be released by the reassembly buffer, causing a crash, as the data is now not valid anymore.
Testing procedure
With a board of your choice (preferably
native, as this test due to anethosbug [#12264] skips some tests for non-native boards):if feee568 is reverted, the test fails.
Issues/PRs references
Follow-up on #12375.