[PATCH nf] netfilter: ebtables: terminate table name before find_table_lock()

[Xiang Mei <xmei5@asu.edu>]

update_counters() and compat_update_counters() forward a user-supplied
32-byte table name to find_table_lock() without NUL-terminating it. On a
lookup miss, find_inlist_lock() calls try_then_request_module(..., "%s%s",
"ebtable_", name), and vsnprintf() reads past the name field and the
stack object until it hits a zero byte.

  BUG: KASAN: stack-out-of-bounds in string (lib/vsprintf.c:648 lib/vsprintf.c:730)
  Read of size 1 at addr ffff8880119dfb20 by task exploit/147
  Call Trace:
  ...
   string (lib/vsprintf.c:648 lib/vsprintf.c:730)
   vsnprintf (lib/vsprintf.c:2945)
   __request_module (kernel/module/kmod.c:150)
   do_update_counters.isra.0 (net/bridge/netfilter/ebtables.c:371 net/bridge/netfilter/ebtables.c:380)
   update_counters (net/bridge/netfilter/ebtables.c:1440)
   do_ebt_set_ctl (net/bridge/netfilter/ebtables.c:2573)
   nf_setsockopt (net/netfilter/nf_sockopt.c:101)
   ip_setsockopt (net/ipv4/ip_sockglue.c:1424)
   raw_setsockopt (net/ipv4/raw.c:847)
   __sys_setsockopt (net/socket.c:2393)
  ...

compat_do_replace() shares the same unterminated name via
compat_copy_ebt_replace_from_user(); terminate it there too so all
find_table_lock() callers behave alike. The other callers already
terminate the name after the copy.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: 81e675c227ec ("netfilter: ebtables: add CONFIG_COMPAT support")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@asu.edu>
---
 net/bridge/netfilter/ebtables.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index f20c039e44c8..5b74ff827493 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1434,6 +1434,8 @@ static int update_counters(struct net *net, sockptr_t arg, unsigned int len)
 	if (copy_from_sockptr(&hlp, arg, sizeof(hlp)))
 		return -EFAULT;
 
+	hlp.name[sizeof(hlp.name) - 1] = '\0';
+
 	if (len != sizeof(hlp) + hlp.num_counters * sizeof(struct ebt_counter))
 		return -EINVAL;
 
@@ -2273,6 +2275,8 @@ static int compat_copy_ebt_replace_from_user(struct ebt_replace *repl,
 
 	memcpy(repl, &tmp, offsetof(struct ebt_replace, hook_entry));
 
+	repl->name[sizeof(repl->name) - 1] = '\0';
+
 	/* starting with hook_entry, 32 vs. 64 bit structures are different */
 	for (i = 0; i < NF_BR_NUMHOOKS; i++)
 		repl->hook_entry[i] = compat_ptr(tmp.hook_entry[i]);
@@ -2395,6 +2399,8 @@ static int compat_update_counters(struct net *net, sockptr_t arg,
 	if (copy_from_sockptr(&hlp, arg, sizeof(hlp)))
 		return -EFAULT;
 
+	hlp.name[sizeof(hlp.name) - 1] = '\0';
+
 	/* try real handler in case userland supplied needed padding */
 	if (len != sizeof(hlp) + hlp.num_counters * sizeof(struct ebt_counter))
 		return update_counters(net, arg, len);
-- 
2.43.0