nfsd4: check for negative dentry before use in nfsv4 readdir
After 2f9092e1020246168b1309b35e085ecd7ff9ff72 "Fix i_mutex vs. readdir
handling in nfsd" (and 14f7dd63 "Copy XFS readdir hack into nfsd code"),
an entry may be removed between the first mutex_unlock and the second
mutex_lock. In this case, lookup_one_len() will return a negative
dentry. Check for this case to avoid a NULL dereference.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Reviewed-by: J. R. Okajima <hooanon05@yahoo.co.jp>
Cc: stable@kernel.org
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index b820c31..b73549d 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2214,6 +2214,15 @@
dentry = lookup_one_len(name, cd->rd_fhp->fh_dentry, namlen);
if (IS_ERR(dentry))
return nfserrno(PTR_ERR(dentry));
+ if (!dentry->d_inode) {
+ /*
+ * nfsd_buffered_readdir drops the i_mutex between
+ * readdir and calling this callback, leaving a window
+ * where this directory entry could have gone away.
+ */
+ dput(dentry);
+ return nfserr_noent;
+ }
exp_get(exp);
/*
@@ -2276,6 +2285,7 @@
struct nfsd4_readdir *cd = container_of(ccd, struct nfsd4_readdir, common);
int buflen;
__be32 *p = cd->buffer;
+ __be32 *cookiep;
__be32 nfserr = nfserr_toosmall;
/* In nfsv4, "." and ".." never make it onto the wire.. */
@@ -2292,7 +2302,7 @@
goto fail;
*p++ = xdr_one; /* mark entry present */
- cd->offset = p; /* remember pointer */
+ cookiep = p;
p = xdr_encode_hyper(p, NFS_OFFSET_MAX); /* offset of next entry */
p = xdr_encode_array(p, name, namlen); /* name length & name */
@@ -2306,6 +2316,8 @@
goto fail;
case nfserr_dropit:
goto fail;
+ case nfserr_noent:
+ goto skip_entry;
default:
/*
* If the client requested the RDATTR_ERROR attribute,
@@ -2324,6 +2336,8 @@
}
cd->buflen -= (p - cd->buffer);
cd->buffer = p;
+ cd->offset = cookiep;
+skip_entry:
cd->common.err = nfs_ok;
return 0;
fail:
