From ce587e07ba2e25b5c9d286849885b82676661f3e Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Fri, 16 Apr 2010 16:22:52 -0400 Subject: [PATCH] NFS: Prevent the mount code from looping forever on broken exports 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 --- fs/nfs/super.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) diff --git a/fs/nfs/super.c b/fs/nfs/super.c index 98d1ab8bf8f..50c6c282ba4 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -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: -- 2.43.2