xen/hypfs: fix writing of custom parameter

Today the maximum allowed data length for writing a hypfs node is
tested in the generic hypfs_write() function. For custom runtime
parameters this might be wrong, as the maximum allowed size is derived
from the buffer holding the current setting, while there might be ways
to set the parameter needing more characters than the minimal
representation of that value.

One example for this is the "ept" parameter. Its value buffer is sized
to be able to hold the string "exec-sp=0" or "exec-sp=1", while it is
allowed to use e.g. "no-exec-sp" or "exec-sp=yes" for setting it.

Fix that by moving the length check one level down to the type
specific write function.

In order to avoid allocation of arbitrary sized buffers use a new
MAX_PARAM_SIZE macro as an upper limit for custom writes. The value
of MAX_PARAM_SIZE is the same as the limit in parse_params() for a
single parameter.

Fixes: a659d7cab9af ("xen: add runtime parameter access support to hypfs")
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/common/hypfs.c b/xen/common/hypfs.c
index b74c228191692af5aa48ce86cf67f1ade4edc277..8e932b5cf981f494ecf4a808def6038ff28bb82a 100644 (file)
--- a/xen/common/hypfs.c
+++ b/xen/common/hypfs.c
@@ -297,7 +297,9 @@ int hypfs_write_leaf(struct hypfs_entry_leaf *leaf,
     int ret;
 
     ASSERT(this_cpu(hypfs_locked) == hypfs_write_locked);
-    ASSERT(ulen <= leaf->e.max_size);
+
+    if ( ulen > leaf->e.max_size )
+        return -ENOSPC;
 
     if ( leaf->e.type != XEN_HYPFS_TYPE_STRING &&
          leaf->e.type != XEN_HYPFS_TYPE_BLOB && ulen != leaf->e.size )
@@ -356,6 +358,10 @@ int hypfs_write_custom(struct hypfs_entry_leaf *leaf,
 
     ASSERT(this_cpu(hypfs_locked) == hypfs_write_locked);
 
+    /* Avoid oversized buffer allocation. */
+    if ( ulen > MAX_PARAM_SIZE )
+        return -ENOSPC;
+
     buf = xzalloc_array(char, ulen);
     if ( !buf )
         return -ENOMEM;
@@ -386,9 +392,6 @@ static int hypfs_write(struct hypfs_entry *entry,
 
     ASSERT(entry->max_size);
 
-    if ( ulen > entry->max_size )
-        return -ENOSPC;
-
     l = container_of(entry, struct hypfs_entry_leaf, e);
 
     return entry->write(l, uaddr, ulen);

diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 9de07b7ac53c4c1a894cebb7d1e8af8cce2be1ef..c3a943f077655d0acb96c53ff4406fe7a0bde788 100644 (file)
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -57,7 +57,7 @@ static int assign_integer_param(const struct kernel_param *param, uint64_t val)
 static int parse_params(const char *cmdline, const struct kernel_param *start,
                         const struct kernel_param *end)
 {
-    char opt[128], *optval, *optkey, *q;
+    char opt[MAX_PARAM_SIZE], *optval, *optkey, *q;
     const char *p = cmdline, *key;
     const struct kernel_param *param;
     int rc, final_rc = 0;

diff --git a/xen/include/xen/param.h b/xen/include/xen/param.h
index f4be944248df3b679e09e3d363ee5c9d1cf75a27..d0409d3a0e7f33bf736c5d1d9ed6fbd9447b9d24 100644 (file)
--- a/xen/include/xen/param.h
+++ b/xen/include/xen/param.h
@@ -26,6 +26,9 @@ struct kernel_param {
     } par;
 };
 
+/* Maximum length of a single parameter string. */
+#define MAX_PARAM_SIZE 128
+
 extern const struct kernel_param __setup_start[], __setup_end[];
 
 #define __param(att)      static const att \