[PATCH] r/o bind mounts: elevate write count for xattr_permission() callers

This basically audits the callers of xattr_permission(), which calls
permission() and can perform writes to the filesystem.

[AV: add missing parts - removexattr() and nfsd posix acls, plug for a leak
spotted by Miklos]

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 10 insertions, 1 deletions

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index c593db047d8b..c309c881bd4e 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -658,14 +658,19 @@ nfsd4_setattr(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
                         return status;
                 }
         }
+        status = mnt_want_write(cstate->current_fh.fh_export->ex_path.mnt);
+        if (status)
+                return status;
         status = nfs_ok;
         if (setattr->sa_acl != NULL)
                 status = nfsd4_set_nfs4_acl(rqstp, &cstate->current_fh,
                                             setattr->sa_acl);
         if (status)
-                return status;
+                goto out;
         status = nfsd_setattr(rqstp, &cstate->current_fh, &setattr->sa_iattr,
                                 0, (time_t)0);
+out:
+        mnt_drop_write(cstate->current_fh.fh_export->ex_path.mnt);
         return status;
 }
 
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 18a4cc9feeb3..626dfd38528f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -2086,6 +2086,9 @@ nfsd_set_posix_acl(struct svc_fh *fhp, int type, struct posix_acl *acl)
         } else
                 size = 0;
 
+        error = mnt_want_write(fhp->fh_export->ex_path.mnt);
+        if (error)
+                goto getout;
         if (size)
                 error = vfs_setxattr(fhp->fh_dentry, name, value, size, 0);
         else {
@@ -2097,6 +2100,7 @@ nfsd_set_posix_acl(struct svc_fh *fhp, int type, struct posix_acl *acl)
                                 error = 0;
                 }
         }
+        mnt_drop_write(fhp->fh_export->ex_path.mnt);
 
 getout:
         kfree(value);