Messages in this thread Patch in this message | | | From | Sergei Zviagintsev <> | Subject | [PATCH RFC 5/5] kdbus: improve tests on incrementing quota | Date | Sun, 28 Jun 2015 16:17:34 +0300 |
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1) Rewrite
quota->memory + memory > U32_MAX
as U32_MAX - quota->memory < memory
and provide the comment on why we need that check.
We have no overflow issue in the original expression when size_t is 32-bit because the previous one (available - quota->memory < memory) guarantees that quota->memory + memory doesn't exceed `available' which is <= U32_MAX in that case.
But lets stay explicit rather than implicit, it would save us from describing HOW the code works.
2) Add WARN_ON when quota->msgs > KDBUS_CONN_MAX_MSGS
This is somewhat inconsistent, so we need to properly report it.
3) Replace
quota->fds + fds < quota->fds || quota->fds + fds > KDBUS_CONN_MAX_FDS_PER_USER
with
KDBUS_CONN_MAX_FDS_PER_USER - quota->fds < fds
and add explicit WARN_ON in the case quota->fds > KDBUS_CONN_MAX_FDS_PER_USER.
Reading the code one can assume that the first expression is there to ensure that we won't have an overflow in quota->fds after quota->fds += fds, but what it really does is testing for size_t overflow in `quota->fds + fds' to be safe in the second expression (as fds is size_t, quota->fds is converted to bigger type).
Rewrite it in more obvious way. KDBUS_CONN_MAX_FDS_PER_USER is checked at compile time to fill in quota->fds type (there is BUILD_BUG_ON), so no further checks for quota->fds overflow are needed.
Signed-off-by: Sergei Zviagintsev <sergei@s15v.net> --- ipc/kdbus/connection.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/ipc/kdbus/connection.c b/ipc/kdbus/connection.c index 12e32de310f5..6556a0f9d44c 100644 --- a/ipc/kdbus/connection.c +++ b/ipc/kdbus/connection.c @@ -701,13 +701,21 @@ int kdbus_conn_quota_inc(struct kdbus_conn *c, struct kdbus_user *u, available = (available - accounted + quota->memory) / 3; if (available < quota->memory || - available - quota->memory < memory || - quota->memory + memory > U32_MAX) + available - quota->memory < memory) return -ENOBUFS; - if (quota->msgs >= KDBUS_CONN_MAX_MSGS) + + /* + * available is size_t and thus it could be greater than U32_MAX. + * Ensure that quota->memory won't overflow. + */ + if (U32_MAX - quota->memory < memory) + return -ENOBUFS; + + if (WARN_ON(quota->msgs > KDBUS_CONN_MAX_MSGS) || + quota->msgs == KDBUS_CONN_MAX_MSGS) return -ENOBUFS; - if (quota->fds + fds < quota->fds || - quota->fds + fds > KDBUS_CONN_MAX_FDS_PER_USER) + if (WARN_ON(quota->fds > KDBUS_CONN_MAX_FDS_PER_USER) || + KDBUS_CONN_MAX_FDS_PER_USER - quota->fds < fds) return -EMFILE; quota->memory += memory; -- 1.8.3.1
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