gnrc_pktbuf_static: fix alignment issue / leaks #9434
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This fixes an alignment issue I encountered in the static version of
the packet buffer.
The bug is caused by a race-condition where a certain order of
operations leads to a chunk being released according to the
byte-alignment of the platform, but overlapping potential space for
a future `_unused_t` struct e.g. (x mark allocated regions):
Future leak of size sizeof(_unused_t) Time
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Sadly, I wasn't able to create a reproducable unittest that show-cases
this corner-case, since I don't understand the order of operations that
cause this one 100%, but the bug is reproducable (but also not
reliably) by sending large (i.e. fragmented) packets to a 6Lo-enabled
host from more than 1 host simultaneously (use `gnrc_pktbuf_cmd` to
check).
By making the size of `_unused_t` the only condition for alignment,
this bug is fixed.
miri64
added
Type: bug
cgundogan
approved these changes
Jul 2, 2018
cgundogan
added
the
CI: ready for build
|
tested on the iotlab-testbed using three iotlab-m3 nodes in the paris site. Can confirm the leak pre-PR and the fix post-PR. ACK and GO. |
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Thanks! |
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Contribution description
This fixes an alignment issue I encountered in the static version of the packet buffer.
The bug is caused by a race-condition where a certain order of operations leads to a chunk being released according to the byte-alignment of the platform, but overlapping potential space for a future
_unused_tstruct e.g. (x mark allocated regions):Sadly, I wasn't able to create a reproducable unittest that show-cases this corner-case, since I don't understand the order of operations that cause this one 100%, but the bug is reproducable (but also not
reliably) by sending large (i.e. fragmented) packets to a 6Lo-enabled host from more than 1 host simultaneously (use
gnrc_pktbuf_cmdto check but don't confuse incomplete datagrams for leaks; see #9424 for faster clean-up of those). I ran this test twice for an hour with this PR before submitting, to make sure this fixes the issue.By making the size of
_unused_tthe only condition for alignment, this bug is fixed.This PR also contains some optimizations that can be done due to the new alignment (acfe57a)
Issues/PRs references
#9424 can simplify testing a bit