lkml.org 
[lkml]   [2020]   [Aug]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] stackleak: Fix a race between stack erasing sysctl handlers
Date
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
\
 
 \ /
  Last update: 2020-08-22 12:11    [W:0.025 / U:3.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site