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authorDavid Howells <dhowells@redhat.com>2011-08-16 15:31:30 +0100
committerAl Viro <viro@zeniv.linux.org.uk>2011-11-20 23:04:27 -0500
commitdd179946db2493646955efc112d73c85b3cafcb1 (patch)
tree59203e419cf14e4a28e3ede7cb32a00d34bd0f8e
parentf1fd306a91f875e65af0e04855b23adda6831ac9 (diff)
downloadlinux-dd179946db2493646955efc112d73c85b3cafcb1.tar.bz2
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 <viro@zeniv.linux.org.uk> 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 <dhowells@redhat.com> Acked-by: Sachin Prabhu <sprabhu@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/dcache.c11
1 files changed, 10 insertions, 1 deletions
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 <linux/bit_spinlock.h>
#include <linux/rculist_bl.h>
#include <linux/prefetch.h>
+#include <linux/ratelimit.h>
#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;
}
}