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ipc/util.c: use ipc_rcu_putref() for failues in ipc_addid()

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ipc_addid() is impossible to use:
- for certain failures, the caller must not use ipc_rcu_putref(),
  because the reference counter is not yet initialized.
- for other failures, the caller must use ipc_rcu_putref(),
  because parallel operations could be ongoing already.

The patch cleans that up, by initializing the refcount early, and by
modifying all callers.

The issues is related to the finding of
[email protected]: syzbot found an
issue with reading kern_ipc_perm.seq, here both read and write to already
released memory could happen.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Manfred Spraul <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Manfred Spraul 2018-08-21 22:01:29 -07:00 • committed by Linus Torvalds
commit 39cfffd774
4 changed files with 12 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

10
ipc/util.c
View file

@ -251,7 +251,9 @@ static inline int ipc_idr_alloc(struct ipc_ids *ids, struct kern_ipc_perm *new)
* Add an entry 'new' to the ipc ids idr. The permissions object is
* initialised and the first free entry is set up and the id assigned
* is returned. The 'new' entry is returned in a locked state on success.
*
* On failure the entry is not locked and a negative err-code is returned.
* The caller must use ipc_rcu_putref() to free the identifier.
*
* Called with writer ipc_ids.rwsem held.
*/
@ -261,6 +263,9 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
kgid_t egid;
int idx, err;
/* 1) Initialize the refcount so that ipc_rcu_putref works */
refcount_set(&new->refcount, 1);
if (limit > IPCMNI)
limit = IPCMNI;
@ -269,9 +274,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
idr_preload(GFP_KERNEL);
refcount_set(&new->refcount, 1);
spin_lock_init(&new->lock);
new->deleted = false;
rcu_read_lock();
spin_lock(&new->lock);
@ -279,6 +282,8 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
new->cuid = new->uid = euid;
new->gid = new->cgid = egid;
new->deleted = false;
idx = ipc_idr_alloc(ids, new);
idr_preload_end();
@ -291,6 +296,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int limit)
}
}
if (idx < 0) {
new->deleted = true;
spin_unlock(&new->lock);
rcu_read_unlock();
return idx;