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

1 files changed, 15 insertions, 1 deletions

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index b820c311931c..b73549d293be 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2214,6 +2214,15 @@ nfsd4_encode_dirent_fattr(struct nfsd4_readdir *cd,
         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 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
         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 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
                 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 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
                 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 @@ nfsd4_encode_dirent(void *ccdv, const char *name, int namlen,
         }
         cd->buflen -= (p - cd->buffer);
         cd->buffer = p;
+        cd->offset = cookiep;
+skip_entry:
         cd->common.err = nfs_ok;
         return 0;
 fail: