[PATCH v3] kernel: kallsyms: memory override issue, need check destinationbuffer length

From: Chen Gang
Date: Mon Apr 15 2013 - 00:48:55 EST



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@xxxxxxxxxxx>
---
kernel/kallsyms.c | 26 ++++++++++++++++++--------
1 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 2169fee..3127ad5 100644
--- 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;
}
--
1.7.7.6
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