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 <ser...@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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