File 5f5b6b7a-hypfs-fix-custom-param-writes.patch of Package xen

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File 5f5b6b7a-hypfs-fix-custom-param-writes.patch of Package xen (Revision b89aae774d156060fdc2d9632be8ab2b)

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# Commit b4e41b1750d550bf2b1ccf97ee46f4f682bdbb62
# Date 2020-09-11 14:20:10 +0200
# Author Juergen Gross <jgross@suse.com>
# Committer Jan Beulich <jbeulich@suse.com>
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>

--- a/xen/common/hypfs.c
+++ b/xen/common/hypfs.c
@@ -297,7 +297,9 @@ int hypfs_write_leaf(struct hypfs_entry_
     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_entr
 
     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_entr
 
     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);
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -57,7 +57,7 @@ static int assign_integer_param(const st
 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;
--- 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 \

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File 5f5b6b7a-hypfs-fix-custom-param-writes.patch of Package xen (Revision b89aae774d156060fdc2d9632be8ab2b)

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