kernel: kallsyms: memory override issue, need check destination buffer length

  We don't export any symbols > 128 characters, but if we did then
  kallsyms_expand_symbol() would overflow the buffer handed to it.
  So we need check destination buffer length when copying.

  the related test:
    if we define an EXPORT function which name more than 128.
    will panic when call kallsyms_lookup_name by init_kprobes on booting.
    after check the length (provide this patch), it is ok.

  Implementaion:
    add additional destination buffer length parameter (maxlen)
    if uncompressed string is too long (>= maxlen), it will be truncated.
    not check the parameters whether valid, since it is a static function.

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 2169fee..3127ad5 100644 (file)
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -84,9 +84,11 @@ static int is_ksym_addr(unsigned long addr)
 
 /*
  * Expand a compressed symbol data into the resulting uncompressed string,
+ * if uncompressed string is too long (>= maxlen), it will be truncated,
  * given the offset to where the symbol is in the compressed stream.
  */
-static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
+static unsigned int kallsyms_expand_symbol(unsigned int off,
+                                          char *result, size_t maxlen)
 {
        int len, skipped_first = 0;
        const u8 *tptr, *data;
@@ -113,15 +115,20 @@ static unsigned int kallsyms_expand_symbol(unsigned int off, char *result)
 
                while (*tptr) {
                        if (skipped_first) {
+                               if (maxlen <= 1)
+                                       goto tail;
                                *result = *tptr;
                                result++;
+                               maxlen--;
                        } else
                                skipped_first = 1;
                        tptr++;
                }
        }
 
-       *result = '\0';
+tail:
+       if (maxlen)
+               *result = '\0';
 
        /* Return to offset to the next symbol. */
        return off;
@@ -176,7 +183,7 @@ unsigned long kallsyms_lookup_name(const char *name)
        unsigned int off;
 
        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
-               off = kallsyms_expand_symbol(off, namebuf);
+               off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 
                if (strcmp(namebuf, name) == 0)
                        return kallsyms_addresses[i];
@@ -195,7 +202,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
        int ret;
 
        for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
-               off = kallsyms_expand_symbol(off, namebuf);
+               off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
                ret = fn(data, namebuf, NULL, kallsyms_addresses[i]);
                if (ret != 0)
                        return ret;
@@ -294,7 +301,8 @@ const char *kallsyms_lookup(unsigned long addr,
 
                pos = get_symbol_pos(addr, symbolsize, offset);
                /* Grab name */
-               kallsyms_expand_symbol(get_symbol_offset(pos), namebuf);
+               kallsyms_expand_symbol(get_symbol_offset(pos),
+                                      namebuf, KSYM_NAME_LEN);
                if (modname)
                        *modname = NULL;
                return namebuf;
@@ -315,7 +323,8 @@ int lookup_symbol_name(unsigned long addr, char *symname)
 
                pos = get_symbol_pos(addr, NULL, NULL);
                /* Grab name */
-               kallsyms_expand_symbol(get_symbol_offset(pos), symname);
+               kallsyms_expand_symbol(get_symbol_offset(pos),
+                                      symname, KSYM_NAME_LEN);
                return 0;
        }
        /* See if it's in a module. */
@@ -333,7 +342,8 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 
                pos = get_symbol_pos(addr, size, offset);
                /* Grab name */
-               kallsyms_expand_symbol(get_symbol_offset(pos), name);
+               kallsyms_expand_symbol(get_symbol_offset(pos),
+                                      name, KSYM_NAME_LEN);
                modname[0] = '\0';
                return 0;
        }
@@ -463,7 +473,7 @@ static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 
        iter->type = kallsyms_get_symbol_type(off);
 
-       off = kallsyms_expand_symbol(off, iter->name);
+       off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 
        return off - iter->nameoff;
 }