netfilter: copy less data to the user

Smatch complains that we copy too much data to the user in ebtables. We copied EBT_FUNCTION_MAXNAMELEN (32) characters to the user here, but "m->u.match->name" has XT_EXTENSION_MAXNAMELEN (29) characters.

I'm not sure if this is a bug where someone got confused with m->u.name which has 32 characters or if this is done for backwards compatability.

net/bridge/netfilter/ebtables.c +3 -4

index 59ca00e..6bcb31d 100644
@@ -1323,7 +1323,7 @@ static inline int ebt_make_matchname(const struct ebt_entry_match *m,
     const char *base, char __user *ubase)
 {
 	char __user *hlp = ubase + ((char *)m - base);
-	if (copy_to_user(hlp, m->u.match->name, EBT_FUNCTION_MAXNAMELEN))
+	if (copy_to_user(hlp, m->u.match->name, XT_EXTENSION_MAXNAMELEN))
 		return -EFAULT;
 	return 0;
 }

@@ -1332,7 +1332,7 @@ static inline int ebt_make_watchername(const struct ebt_entry_watcher *w,
     const char *base, char __user *ubase)
 {
 	char __user *hlp = ubase + ((char *)w - base);
-	if (copy_to_user(hlp , w->u.watcher->name, EBT_FUNCTION_MAXNAMELEN))
+	if (copy_to_user(hlp , w->u.watcher->name, XT_EXTENSION_MAXNAMELEN))
 		return -EFAULT;
 	return 0;
 }

@@ -1356,7 +1356,7 @@ ebt_make_names(struct ebt_entry *e, const char *base, char __user *ubase)
 	ret = EBT_WATCHER_ITERATE(e, ebt_make_watchername, base, ubase);
 	if (ret != 0)
 		return ret;
-	if (copy_to_user(hlp, t->u.target->name, EBT_FUNCTION_MAXNAMELEN))
+	if (copy_to_user(hlp, t->u.target->name, XT_EXTENSION_MAXNAMELEN))
 		return -EFAULT;
 	return 0;
 }
--

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Am 14.07.2010 23:04, schrieb Dan Carpenter:

Quoted 4 lines

Smatch complains that we copy too much data to the user in ebtables. We copied EBT_FUNCTION_MAXNAMELEN (32) characters to the user here, but "m->u.match->name" has XT_EXTENSION_MAXNAMELEN (29) characters.

Quoted 2 lines

I'm not sure if this is a bug where someone got confused with m->u.name which has 32 characters or if this is done for backwards compatability.

Looking at ebtables.h, ebt_entry_match->name uses EBT_FUNCTION_MAXNAMELEN, which is 32 bytes. Where did you get XT_EXTENSION_MAXNAMELEN from?

Quoted 8 lines

Am 14.07.2010 23:04, schrieb Dan Carpenter:

Quoted 6 lines

Smatch complains that we copy too much data to the user in ebtables. We copied EBT_FUNCTION_MAXNAMELEN (32) characters to the user here, but "m->u.match->name" has XT_EXTENSION_MAXNAMELEN (29) characters.

I'm not sure if this is a bug where someone got confused with m->u.name which has 32 characters or if this is done for backwards compatability.

Quoted 4 lines

Looking at ebtables.h, ebt_entry_match->name uses EBT_FUNCTION_MAXNAMELEN, which is 32 bytes. Where did you get XT_EXTENSION_MAXNAMELEN from?

Exactly. ebt_entry_match->u.name uses EBT_FUNCTION_MAXNAMELEN but this is from ebt_entry_match->u.match->name which is type struct xt_match.

But it looks like we're exporting struct ebt_match which also uses EBT_FUNCTION_MAXNAMELEN. So maybe the fix is to copy ->u.name instead of ->u.match->name.

Am 15.07.2010 12:16, schrieb Dan Carpenter:

Quoted 9 lines · Patrick McHardy

Quoted 8 lines

Am 14.07.2010 23:04, schrieb Dan Carpenter:

Quoted 6 lines

Smatch complains that we copy too much data to the user in ebtables. We copied EBT_FUNCTION_MAXNAMELEN (32) characters to the user here, but "m->u.match->name" has XT_EXTENSION_MAXNAMELEN (29) characters.

I'm not sure if this is a bug where someone got confused with m->u.name which has 32 characters or if this is done for backwards compatability.

Quoted 7 lines

Quoted 4 lines

Looking at ebtables.h, ebt_entry_match->name uses EBT_FUNCTION_MAXNAMELEN, which is 32 bytes. Where did you get XT_EXTENSION_MAXNAMELEN from?

Exactly. ebt_entry_match->u.name uses EBT_FUNCTION_MAXNAMELEN but this is from ebt_entry_match->u.match->name which is type struct xt_match.

Right, I see.

Quoted 3 lines

But it looks like we're exporting struct ebt_match which also uses EBT_FUNCTION_MAXNAMELEN. So maybe the fix is to copy ->u.name instead of ->u.match->name.

That name is not valid within the kernel, the union contains the xt_match pointer. So your patch seems correct, but we probably also need to adjust ebtables userspace.

Jan?