* [PATCH] stackleak: Fix a race between stack erasing sysctl handlers
@ 2020-08-22 10:08 Muchun Song
0 siblings, 0 replies; only message in thread
From: Muchun Song @ 2020-08-22 10:08 UTC (permalink / raw)
To: keescook, mhiramat, rostedt, alex.popov, miguel.ojeda.sandonis
Cc: linux-kernel, Muchun Song
There is a race between the assignment of `table->data` and write value
to the pointer of `table->data` in the __do_proc_doulongvec_minmax().
Fix this by duplicating the `table`, and only update the duplicate of
it.
Fixes: 964c9dff0091 ("stackleak: Allow runtime disabling of kernel stack erasing")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
kernel/stackleak.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index a8fc9ae1d03d..fd95b87478ff 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -25,10 +25,15 @@ int stack_erasing_sysctl(struct ctl_table *table, int write,
int ret = 0;
int state = !static_branch_unlikely(&stack_erasing_bypass);
int prev_state = state;
+ struct ctl_table dup_table = *table;
- table->data = &state;
- table->maxlen = sizeof(int);
- ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ /*
+ * In order to avoid races with __do_proc_doulongvec_minmax(), we
+ * can duplicate the @table and alter the duplicate of it.
+ */
+ dup_table.data = &state;
+ dup_table.maxlen = sizeof(int);
+ ret = proc_dointvec_minmax(&dup_table, write, buffer, lenp, ppos);
state = !!state;
if (ret || !write || state == prev_state)
return ret;
--
2.11.0
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