pppoe: disc: document who holds references to the net object #141
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While working on another patch, I had a bug that *seemed* to be related to a use-after-free on the net structure, leading to a faulty patch removing the disc_stop refcount decrement, as I missed that the init_net function initialized the refcount to 1 and not 0. The bug was in my code. This patch adds simple comments the reference handling to make it a bit more obvious what is going on. Signed-off-by: Simon Chopin <[email protected]>
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OK, this patch is actually wrong. I'll replace it with a patch that only adds comments and edit the title and description. Feel free to directly close the PR if you think them superfluous. |
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Dear @laarmen, Can you open a PR at "good" place: Thanks in advance. |
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REVISED PATCH
While working on another patch, I had a bug that seemed to be related
to a use-after-free on the net structure, leading to a faulty patch
removing the disc_stop refcount decrement, as I missed that the init_net
function initialized the refcount to 1 and not 0. The bug was in my
code.
This patch adds simple comments the reference handling to make it a bit
more obvious what is going on.
INITIAL VERSION
pppoe: disc: do not free the net struct in disc_stop
Assuming there is only one server associated with the current net
object, freeing the net object at the end of disc_stop could potentially
create a use-after-free error since before that, we queued an
asynchronous call to _serv_stop, which in turn calls pppoe_disc_stop.
Since pppoe_disc_stop acquires a pointer to the net object at the
beginning of its run, and uses it all throughout as part of its locking,
having free_net running alongside could result in the memory backing the
lock being freed while the code is running.