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>

1 files changed, 13 insertions, 4 deletions

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 39df95a0ec25..b1cf6bf4b41d 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -22,6 +22,7 @@
 
 #include <linux/errno.h>
 
+EXPORT_SYMBOL(posix_acl_init);
 EXPORT_SYMBOL(posix_acl_alloc);
 EXPORT_SYMBOL(posix_acl_clone);
 EXPORT_SYMBOL(posix_acl_valid);
@@ -32,6 +33,16 @@ EXPORT_SYMBOL(posix_acl_chmod_masq);
 EXPORT_SYMBOL(posix_acl_permission);
 
 /*
+ * Init a fresh posix_acl
+ */
+void
+posix_acl_init(struct posix_acl *acl, int count)
+{
+        atomic_set(&acl->a_refcount, 1);
+        acl->a_count = count;
+}
+
+/*
  * Allocate a new ACL with the specified number of entries.
  */
 struct posix_acl *
@@ -40,10 +51,8 @@ posix_acl_alloc(int count, gfp_t flags)
         const size_t size = sizeof(struct posix_acl) +
                             count * sizeof(struct posix_acl_entry);
         struct posix_acl *acl = kmalloc(size, flags);
-        if (acl) {
-                atomic_set(&acl->a_refcount, 1);
-                acl->a_count = count;
-        }
+        if (acl)
+                posix_acl_init(acl, count);
         return acl;
 }