From dd179946db2493646955efc112d73c85b3cafcb1 Mon Sep 17 00:00:00 2001 From: David Howells Date: Tue, 16 Aug 2011 15:31:30 +0100 Subject: [PATCH] VFS: Log the fact that we've given ELOOP rather than creating a loop To prevent an NFS server from being used to create a directory loop in an NFS superblock on the client, the following patch was committed: commit 1836750115f20b774e55c032a3893e8c5bdf41ed Author: Al Viro Date: Tue Jul 12 21:42:24 2011 -0400 Subject: fix loop checks in d_materialise_unique() This causes ELOOP to be reported to anyone trying to access the dentry that would otherwise cause the kernel to complete the loop. However, no indication is given to the caller as to why an operation that ought to work doesn't. The fault is with the kernel, which doesn't want to try and solve the problem as it gets horrendously messy if there's another mountpoint somewhere in the trees being spliced that can't be moved[*]. [*] The real problem is that we don't handle the excision of a subtree that gets moved _out_ of what we can see. This can happen on the server where a directory is merely moved between two other dirs on the same filesystem, but where destination dir is not accessible by the client. So, given the choice to return ELOOP rather than trying to reconfigure the dentry tree, we should give the caller some indication of why they aren't being allowed to make what should be a legitimate request and log a message. Signed-off-by: David Howells Acked-by: Sachin Prabhu Signed-off-by: Al Viro --- fs/dcache.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index a901c6901bce..10ba92def3f6 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -36,6 +36,7 @@ #include #include #include +#include #include "internal.h" /* @@ -2383,8 +2384,16 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode) actual = __d_unalias(inode, dentry, alias); } write_sequnlock(&rename_lock); - if (IS_ERR(actual)) + if (IS_ERR(actual)) { + if (PTR_ERR(actual) == -ELOOP) + pr_warn_ratelimited( + "VFS: Lookup of '%s' in %s %s" + " would have caused loop\n", + dentry->d_name.name, + inode->i_sb->s_type->name, + inode->i_sb->s_id); dput(alias); + } goto out_nolock; } } -- 2.20.1