NFS: Prevent memory allocation failure in nfsacl_encode()
nfsacl_encode() allocates memory in certain cases. This of course
is not guaranteed to work.
Since commit 9f06c719 "SUNRPC: New xdr_streams XDR encoder API", the
kernel's XDR encoders can't return a result indicating possibly a
failure, so a memory allocation failure in nfsacl_encode() has become
fatal (ie, the XDR code Oopses) in some cases.
However, the allocated memory is a tiny fixed amount, on the order
of 40-50 bytes. We can easily use a stack-allocated buffer for
this, with only a wee bit of nose-holding.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs_common/nfsacl.c b/fs/nfs_common/nfsacl.c
index a3e78bd..84c27d6 100644
--- a/fs/nfs_common/nfsacl.c
+++ b/fs/nfs_common/nfsacl.c
@@ -42,6 +42,11 @@
gid_t gid;
};
+struct nfsacl_simple_acl {
+ struct posix_acl acl;
+ struct posix_acl_entry ace[4];
+};
+
static int
xdr_nfsace_encode(struct xdr_array2_desc *desc, void *elem)
{
@@ -99,17 +104,22 @@
.uid = inode->i_uid,
.gid = inode->i_gid,
};
+ struct nfsacl_simple_acl aclbuf;
int err;
- struct posix_acl *acl2 = NULL;
if (entries > NFS_ACL_MAX_ENTRIES ||
xdr_encode_word(buf, base, entries))
return -EINVAL;
if (encode_entries && acl && acl->a_count == 3) {
- /* Fake up an ACL_MASK entry. */
- acl2 = posix_acl_alloc(4, GFP_KERNEL);
- if (!acl2)
- return -ENOMEM;
+ struct posix_acl *acl2 = &aclbuf.acl;
+
+ /* Avoid the use of posix_acl_alloc(). nfsacl_encode() is
+ * invoked in contexts where a memory allocation failure is
+ * fatal. Fortunately this fake ACL is small enough to
+ * construct on the stack. */
+ memset(acl2, 0, sizeof(acl2));
+ posix_acl_init(acl2, 4);
+
/* Insert entries in canonical order: other orders seem
to confuse Solaris VxFS. */
acl2->a_entries[0] = acl->a_entries[0]; /* ACL_USER_OBJ */
@@ -120,8 +130,6 @@
nfsacl_desc.acl = acl2;
}
err = xdr_encode_array2(buf, base + 4, &nfsacl_desc.desc);
- if (acl2)
- posix_acl_release(acl2);
if (!err)
err = 8 + nfsacl_desc.desc.elem_size *
nfsacl_desc.desc.array_len;