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Subject[PATCH]Fix bug in msgrcv/shmat
Hello, Linux & Alan,

This patch verifies the message queue ID and the shared memory segment
ID for msgrcv and shmat respectively. These IDs consist of a data
structure index value, and a generation number. As data structures are
re-used, the generation number makes it possible to avoid incorrect
data references. The generation numbers are checked via msg_checkid()
and shm_checkid(). The problem is that msgrcv and shmat do not currently
validate the ID. As a result of this, it is possible to reference and
modify the wrong message queue or shared memory segment with the use of
a stale ID.

This patch is against kernel 2.4.9. I tested it and it runs well.
Please apply and CC your comments to me also, thanks.

Mingming Cao
IBM Linux Technology Center

diff -urN -X dontdiff linux/ipc/msg.c linux-tk/ipc/msg.c
--- linux/ipc/msg.c Wed Aug 29 18:26:39 2001
+++ linux-tk/ipc/msg.c Wed Aug 29 18:21:42 2001
@@ -742,6 +742,10 @@
return -EINVAL;
+ err = -EIDRM;
+ if (msg_checkid(msq,msqid))
+ goto out_unlock;
if (ipcperms (&msq->q_perm, S_IRUGO))
goto out_unlock;
diff -urN -X dontdiff linux/ipc/shm.c linux-tk/ipc/shm.c
--- linux/ipc/shm.c Wed Aug 29 18:26:33 2001
+++ linux-tk/ipc/shm.c Wed Aug 29 18:26:15 2001
@@ -606,6 +606,11 @@
shp = shm_lock(shmid);
if(shp == NULL)
return -EINVAL;
+ err = shm_checkid(shp,shmid);
+ if (err) {
+ shm_unlock(shmid);
+ return err;
+ }
if (ipcperms(&shp->shm_perm, acc_mode)) {
return -EACCES;
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