Messages in this thread | | | Date | Sat, 19 Aug 2006 09:48:40 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] NFS: Replace null dentries that appear in readdir's list [try #2] |
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On Fri, 18 Aug 2006 10:38:44 +0100 David Howells <dhowells@redhat.com> wrote:
> NFS: Replace null dentries that appear in readdir's list [try #2] > > From: David Howells <dhowells@redhat.com> > > Have nfs_readdir_lookup() drop and replace any null dentry when it > that gets listed by a READDIR RPC call. > > This can be caused by an optimisation in nfs_lookup() that causes a dentry to > be incorrectly left as negative when mkdir() or similar is aborted by SELinux > mid-procedure. > > This can be triggered by mounting through autofs4 a server:/ NFS share for > which there are other exports available on that server. SELinux also has to > be turned on in enforcing mode to abort mid-flow the mkdir operation performed > by autofs4. > > The problematic sequence of events is this: > > (1) nfs_lookup() is called by sys_mkdirat() -> lookup_create() -> > __lookup_hash() with intent to create exclusively set in the nameidata: > > nd->flags == LOOKUP_CREATE > nd->intent.open.flags == O_EXCL > > (2) nfs_lookup() has an optimisation to avoid going to the server in this > case, presumably since the nfs_mkdir() op or whatever will deal with the > conflict. > > (3) nfs_lookup() returns successfully, leaving the dentry in a negative state, > but attached to the parent directory. > > (4) sys_mkdirat() calls vfs_mkdir() which calls may_create(). may_create() > checks that the directory has MAY_WRITE and MAY_EXEC permissions. > > (5) may_create() calls nfs_permission(), which grants permission. > > (6) may_create() calls security_inode_permission(), which calls SELinux, which > then _DENIES_ permission. > > (7) may_create() fails, and vfs_mkdir() then fails and sys_mkdirat() then > fails (as does sys_mkdir). > > _However_, the new dentry is left in the negative state, with no > consultation of the server. > > (8) The parent directory is listed, and the name of the new dentry is > returned. > > (9) stat on the new dentry fails (because it's negative), and "ls -l" returns > "?---------" as the file type and mode. > > This fix makes step (8) replace the dentry looked up in steps (1) - (3). >
The funny-looking dentries in /net/bix have gone away.
But `ls -l /net/bix/usr/src' doesn't mount bix:/usr/src. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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