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fsnotify: Fix NULL ptr deref in fanotify_get_fsid()

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fanotify_get_fsid() is reading mark->connector->fsid under srcu. It can
happen that it sees mark not fully initialized or mark that is already
detached from the object list. In these cases mark->connector
can be NULL leading to NULL ptr dereference. Fix the problem by
being careful when reading mark->connector and check it for being NULL.
Also use WRITE_ONCE when writing the mark just to prevent compiler from
doing something stupid.

Reported-by: syzbot+15927486a4f1bfcbaf91@syzkaller.appspotmail.com
Fixes: 77115225ac ("fanotify: cache fsid in fsnotify_mark_connector")
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Jan Kara 2019-04-24 18:39:57 +02:00
parent ba25b50d58
commit b1da6a5187
2 changed files with 18 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
fs/notify/fanotify/fanotify.c
View File

@ -346,10 +346,16 @@ static __kernel_fsid_t fanotify_get_fsid(struct fsnotify_iter_info *iter_info)
__kernel_fsid_t fsid = {}; __kernel_fsid_t fsid = {};
fsnotify_foreach_obj_type(type) { fsnotify_foreach_obj_type(type) {
struct fsnotify_mark_connector *conn;
if (!fsnotify_iter_should_report_type(iter_info, type)) if (!fsnotify_iter_should_report_type(iter_info, type))
continue; continue;
fsid = iter_info->marks[type]->connector->fsid; conn = READ_ONCE(iter_info->marks[type]->connector);
/* Mark is just getting destroyed or created? */
if (!conn)
continue;
fsid = conn->fsid;
if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1])) if (WARN_ON_ONCE(!fsid.val[0] && !fsid.val[1]))
continue; continue;
return fsid; return fsid;
@ -408,8 +414,12 @@ static int fanotify_handle_event(struct fsnotify_group *group,
return 0; return 0;
} }
if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) if (FAN_GROUP_FLAG(group, FAN_REPORT_FID)) {
fsid = fanotify_get_fsid(iter_info); fsid = fanotify_get_fsid(iter_info);
/* Racing with mark destruction or creation? */
if (!fsid.val[0] && !fsid.val[1])
return 0;
}
event = fanotify_alloc_event(group, inode, mask, data, data_type, event = fanotify_alloc_event(group, inode, mask, data, data_type,
&fsid); &fsid);

12
fs/notify/mark.c
View File

@ -239,13 +239,13 @@ static void fsnotify_drop_object(unsigned int type, void *objp)
void fsnotify_put_mark(struct fsnotify_mark *mark) void fsnotify_put_mark(struct fsnotify_mark *mark)
{ {
struct fsnotify_mark_connector *conn; struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
void *objp = NULL; void *objp = NULL;
unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED; unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
bool free_conn = false; bool free_conn = false;
/* Catch marks that were actually never attached to object */ /* Catch marks that were actually never attached to object */
if (!mark->connector) { if (!conn) {
if (refcount_dec_and_test(&mark->refcnt)) if (refcount_dec_and_test(&mark->refcnt))
fsnotify_final_mark_destroy(mark); fsnotify_final_mark_destroy(mark);
return; return;
@ -255,10 +255,9 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
* We have to be careful so that traversals of obj_list under lock can * We have to be careful so that traversals of obj_list under lock can
* safely grab mark reference. * safely grab mark reference.
*/ */
if (!refcount_dec_and_lock(&mark->refcnt, &mark->connector->lock)) if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
return; return;
conn = mark->connector;
hlist_del_init_rcu(&mark->obj_list); hlist_del_init_rcu(&mark->obj_list);
if (hlist_empty(&conn->list)) { if (hlist_empty(&conn->list)) {
objp = fsnotify_detach_connector_from_object(conn, &type); objp = fsnotify_detach_connector_from_object(conn, &type);
@ -266,7 +265,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
} else { } else {
__fsnotify_recalc_mask(conn); __fsnotify_recalc_mask(conn);
} }
mark->connector = NULL; WRITE_ONCE(mark->connector, NULL);
spin_unlock(&conn->lock); spin_unlock(&conn->lock);
fsnotify_drop_object(type, objp); fsnotify_drop_object(type, objp);
@ -620,7 +619,7 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark,
/* mark should be the last entry. last is the current last entry */ /* mark should be the last entry. last is the current last entry */
hlist_add_behind_rcu(&mark->obj_list, &last->obj_list); hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
added: added:
mark->connector = conn; WRITE_ONCE(mark->connector, conn);
out_err: out_err:
spin_unlock(&conn->lock); spin_unlock(&conn->lock);
spin_unlock(&mark->lock); spin_unlock(&mark->lock);
@ -808,6 +807,7 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
refcount_set(&mark->refcnt, 1); refcount_set(&mark->refcnt, 1);
fsnotify_get_group(group); fsnotify_get_group(group);
mark->group = group; mark->group = group;
WRITE_ONCE(mark->connector, NULL);
} }
/* /*