net/sctp/diag.c for instance is built into its own separate module (sctp_diag.ko) and requires the use of sctp_endpoint_{hold,put}() in order to prevent a recently found use-after-free issue.
In order to prevent data corruption of the pointer used to take a reference on a specific endpoint, between the time of calling sctp_endpoint_hold() and it returning, the API now returns a pointer to the exact endpoint that was incremented.
For example, in sctp_sock_dump(), we could have the following hunk:
sctp_endpoint_hold(tsp->asoc->ep); ep = tsp->asoc->ep; sk = ep->base.sk lock_sock(ep->base.sk);
It is possible for this task to be swapped out immediately following the call into sctp_endpoint_hold() that would change the address of tsp->asoc->ep to point to a completely different endpoint. This means a reference could be taken to the old endpoint and the new one would be processed without a reference taken, moreover the new endpoint could then be freed whilst still processing as a result, causing a use-after-free.
If we return the exact pointer that was held, we ensure this task processes only the endpoint we have taken a reference to. The resultant hunk now looks like this:
ep = sctp_endpoint_hold(tsp->asoc->ep); sk = ep->base.sk lock_sock(sk);
Cc: Vlad Yasevich vyasevich@gmail.com Cc: Neil Horman nhorman@tuxdriver.com Cc: Marcelo Ricardo Leitner marcelo.leitner@gmail.com Cc: "David S. Miller" davem@davemloft.net Cc: Jakub Kicinski kuba@kernel.org Cc: lksctp developers linux-sctp@vger.kernel.org Cc: "H.P. Yarroll" piggy@acm.org Cc: Karl Knutson karl@athena.chicago.il.us Cc: Jon Grimm jgrimm@us.ibm.com Cc: Xingang Guo xingang.guo@intel.com Cc: Hui Huang hui.huang@nokia.com Cc: Sridhar Samudrala sri@us.ibm.com Cc: Daisy Chang daisyc@us.ibm.com Cc: Ryan Layer rmlayer@us.ibm.com Cc: Kevin Gao kevin.gao@intel.com Cc: linux-sctp@vger.kernel.org Cc: netdev@vger.kernel.org Cc: stable@vger.kernel.org Fixes: 8f840e47f190c ("sctp: add the sctp_diag.c file") Signed-off-by: Lee Jones lee.jones@linaro.org --- include/net/sctp/structs.h | 2 +- net/sctp/endpointola.c | 5 ++++- 2 files changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h index 651bba654d77d..78d71ca56452b 100644 --- a/include/net/sctp/structs.h +++ b/include/net/sctp/structs.h @@ -1380,7 +1380,7 @@ static inline struct sctp_endpoint *sctp_ep(struct sctp_ep_common *base) struct sctp_endpoint *sctp_endpoint_new(struct sock *, gfp_t); void sctp_endpoint_free(struct sctp_endpoint *); void sctp_endpoint_put(struct sctp_endpoint *); -void sctp_endpoint_hold(struct sctp_endpoint *); +struct sctp_endpoint *sctp_endpoint_hold(struct sctp_endpoint *); void sctp_endpoint_add_asoc(struct sctp_endpoint *, struct sctp_association *); struct sctp_association *sctp_endpoint_lookup_assoc( const struct sctp_endpoint *ep, diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c index 48c9c2c7602f7..bdbf74fc7eb4c 100644 --- a/net/sctp/endpointola.c +++ b/net/sctp/endpointola.c @@ -222,10 +222,12 @@ static void sctp_endpoint_destroy(struct sctp_endpoint *ep) }
/* Hold a reference to an endpoint. */ -void sctp_endpoint_hold(struct sctp_endpoint *ep) +struct sctp_endpoint *sctp_endpoint_hold(struct sctp_endpoint *ep) { refcount_inc(&ep->base.refcnt); + return ep; } +EXPORT_SYMBOL_GPL(sctp_endpoint_hold);
/* Release a reference to an endpoint and clean up if there are * no more references. @@ -235,6 +237,7 @@ void sctp_endpoint_put(struct sctp_endpoint *ep) if (refcount_dec_and_test(&ep->base.refcnt)) sctp_endpoint_destroy(ep); } +EXPORT_SYMBOL_GPL(sctp_endpoint_put);
/* Is this the endpoint we are looking for? */ struct sctp_endpoint *sctp_endpoint_is_match(struct sctp_endpoint *ep,