[PATCH] nfsd: fix oops on access from high-numbered ports

["J. Bruce Fields" <bfields@fieldses.org>]

From: J. Bruce Fields <bfields@citi.umich.edu>

This bug was always here, but before my commit 6fa02839bf9412e18e77
("recheck for secure ports in fh_verify"), it could only be triggered by
failure of a kmalloc().  After that commit it could be triggered by a
client making a request from a non-reserved port for access to an export
marked "secure".  (Exports are "secure" by default.)

The result is a struct svc_export with a reference count one to low,
resulting in likely oopses next time the export is accessed.

The reference counting here is not straightforward; a later patch will
clean up fh_verify().

Thanks to Lukas Hejtmanek for the bug report and followup.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Lukas Hejtmanek <xhejtman@ics.muni.cz>
---
 fs/nfsd/nfsfh.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

This is appropriate for 2.6.25, 2.6.24.y, and 2.6.23.y (if it's still
maintained).--b.

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 1eb771d..3e6b3f4 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -232,6 +232,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		fhp->fh_dentry = dentry;
 		fhp->fh_export = exp;
 		nfsd_nr_verified++;
+		cache_get(&exp->h);
 	} else {
 		/*
 		 * just rechecking permissions
@@ -241,6 +242,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		dprintk("nfsd: fh_verify - just checking\n");
 		dentry = fhp->fh_dentry;
 		exp = fhp->fh_export;
+		cache_get(&exp->h);
 		/*
 		 * Set user creds for this exportpoint; necessary even
 		 * in the "just checking" case because this may be a
@@ -252,8 +254,6 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		if (error)
 			goto out;
 	}
-	cache_get(&exp->h);
-
 
 	error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type);
 	if (error)
-- 
1.5.4.rc2.60.gb2e62