: Fix for minor scst_user race

PATCH New Vladislav Bolkhovitin 1 participant 1 message Jan 26, 2009 SCSI

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Vladislav Bolkhovitin

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2009-01-26 18:19 UTC #0 lore raw

PATCH 1/1 : Fix for minor scst_user race

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(-)

src/dev_handlers/scst_user.c +5 -1

Index: scst/src/dev_handlers/scst_user.c
===================================================================
@@ -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);