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NFS: Prevent the mount code from looping forever on broken exports

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Keep a global count of how many referrals that the current task has
traversed on a path lookup. Return ELOOP if the count exceeds
MAX_NESTED_LINKS.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Trond Myklebust 2010-04-16 16:22:52 -04:00
parent 6e94d62993
commit ce587e07ba
1 changed files with 73 additions and 0 deletions
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73
fs/nfs/super.c
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@ -2673,6 +2673,72 @@ out_freepage:
free_page((unsigned long)page);
}
struct nfs_referral_count {
struct list_head list;
const struct task_struct *task;
unsigned int referral_count;
};
static LIST_HEAD(nfs_referral_count_list);
static DEFINE_SPINLOCK(nfs_referral_count_list_lock);
static struct nfs_referral_count *nfs_find_referral_count(void)
{
struct nfs_referral_count *p;
list_for_each_entry(p, &nfs_referral_count_list, list) {
if (p->task == current)
return p;
}
return NULL;
}
#define NFS_MAX_NESTED_REFERRALS 2
static int nfs_referral_loop_protect(void)
{
struct nfs_referral_count *p, *new;
int ret = -ENOMEM;
new = kmalloc(sizeof(*new), GFP_KERNEL);
if (!new)
goto out;
new->task = current;
new->referral_count = 1;
ret = 0;
spin_lock(&nfs_referral_count_list_lock);
p = nfs_find_referral_count();
if (p != NULL) {
if (p->referral_count >= NFS_MAX_NESTED_REFERRALS)
ret = -ELOOP;
else
p->referral_count++;
} else {
list_add(&new->list, &nfs_referral_count_list);
new = NULL;
}
spin_unlock(&nfs_referral_count_list_lock);
kfree(new);
out:
return ret;
}
static void nfs_referral_loop_unprotect(void)
{
struct nfs_referral_count *p;
spin_lock(&nfs_referral_count_list_lock);
p = nfs_find_referral_count();
p->referral_count--;
if (p->referral_count == 0)
list_del(&p->list);
else
p = NULL;
spin_unlock(&nfs_referral_count_list_lock);
kfree(p);
}
static int nfs_follow_remote_path(struct vfsmount *root_mnt,
const char *export_path, struct vfsmount *mnt_target)
{
@ -2690,9 +2756,14 @@ static int nfs_follow_remote_path(struct vfsmount *root_mnt,
if (IS_ERR(ns_private))
goto out_mntput;
ret = nfs_referral_loop_protect();
if (ret != 0)
goto out_put_mnt_ns;
ret = vfs_path_lookup(root_mnt->mnt_root, root_mnt,
export_path, LOOKUP_FOLLOW, nd);
nfs_referral_loop_unprotect();
put_mnt_ns(ns_private);
if (ret != 0)
@ -2710,6 +2781,8 @@ static int nfs_follow_remote_path(struct vfsmount *root_mnt,
kfree(nd);
down_write(&s->s_umount);
return 0;
out_put_mnt_ns:
put_mnt_ns(ns_private);
out_mntput:
mntput(root_mnt);
out_err: