Hi,
There are the following two trivially-fixed races in fs/dlm/config.c:
1. The configfs subsystem semaphore must be held by the caller when
calling config_group_find_obj(). It's needed to walk the subsystem
hierarchy without racing with a simultaneous mkdir(2) or rmdir(2). I
looked around to see if there was some other way we were avoiding this
race, but couldn't find any.
2. get_comm() does hold the subsystem semaphore but lets go too soon --
before grabbing a reference on the found config_item. A concurrent
rmdir(2) could come and release the comm after the up() but before the
config_item_get().
Patch that fixes both these bugs below.
Cheers,
S
PS: For some reason, configfs still uses a struct semaphore (as a binary
semaphore) for configfs_subsystem.su_sem. Someone with free time should
convert that to a struct mutex, say configfs_subsystem.su_mtx -- which is
the preferred way to use (binary) mutexes presently. CC'ing Joel Becker on
this.
---
Fix two races in fs/dlm/config.c:
(1) Grab the configfs subsystem semaphore before calling
config_group_find_obj() in get_space(). This solves a potential race
between get_space() and concurrent mkdir(2) or rmdir(2).
(2) Grab a reference on the found config_item _while_ holding the configfs
subsystem semaphore in get_comm(), and not after it. This solves a
potential race between get_comm() and concurrent rmdir(2).
fs/dlm/config.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
Signed-off-by: Satyam Sharma <[email protected]>
---
diff -ruNp linux-2.6.21.1/fs/dlm/config.c linux-2.6.21.1~patch/fs/dlm/config.c
--- linux-2.6.21.1/fs/dlm/config.c 2007-04-26 08:38:32.000000000 +0530
+++ linux-2.6.21.1~patch/fs/dlm/config.c 2007-05-04 21:08:54.000000000 +0530
@@ -744,9 +744,16 @@ static ssize_t node_weight_write(struct
static struct space *get_space(char *name)
{
+ struct config_item *i;
+
if (!space_list)
return NULL;
- return to_space(config_group_find_obj(space_list, name));
+
+ down(&space_list->cg_subsys->su_sem);
+ i = config_group_find_obj(space_list, name);
+ up(&space_list->cg_subsys->su_sem);
+
+ return to_space(i);
}
static void put_space(struct space *sp)
@@ -772,20 +779,20 @@ static struct comm *get_comm(int nodeid,
if (cm->nodeid != nodeid)
continue;
found = 1;
+ config_item_get(i);
break;
} else {
if (!cm->addr_count ||
memcmp(cm->addr[0], addr, sizeof(*addr)))
continue;
found = 1;
+ config_item_get(i);
break;
}
}
up(&clusters_root.subsys.su_sem);
- if (found)
- config_item_get(i);
- else
+ if (!found)
cm = NULL;
return cm;
}
-
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