This patch fixed race in scst_user module, which can lead to usage of already freed
command. A misbehaving user space handler can make ucmd to get dead immediately
after the lock is released and we should catch it.
Signed-off-by: Vladislav Bolkhovitin <[email protected]>
scst_user.c | 8 ++++++--
1 file changed, 5 insertions(+), 1 deletion(-)
Index: scst/src/dev_handlers/scst_user.c
===================================================================
--- scst/src/dev_handlers/scst_user.c (revision 641)
+++ scst/src/dev_handlers/scst_user.c (working copy)
@@ -1721,6 +1729,7 @@ static int dev_user_reply_get_cmd(struct
kmem_cache_free(user_get_cmd_cachep, cmd);
spin_lock_irq(&dev->cmd_lists.cmd_list_lock);
+again:
res = dev_user_get_next_cmd(dev, &ucmd);
if (res == 0) {
int len;
@@ -1730,12 +1739,15 @@ static int dev_user_reply_get_cmd(struct
* copy of dead data to the user space, which can lead to a
* leak of sensitive information.
*/
- ucmd_get(ucmd);
+ if (unlikely(ucmd_get_check(ucmd))) {
+ /* Oops, this ucmd is already being destroyed. Retry. */
+ goto again;
+ }
spin_unlock_irq(&dev->cmd_lists.cmd_list_lock);
EXTRACHECKS_BUG_ON(ucmd->user_cmd_payload_len == 0);