net: ppp: fix creating PPP pass and active filters

PATCH RESEND In review Christoph Schulz 2 participants 2 messages Jul 16, 2014 – Jul 17, 2014

Subsystems (3)

Networking Network drivers PPP protocol drivers and compressors

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Christoph Schulz

author

2014-07-16 20:10 UTC #0 lore raw

PATCH RESEND 1/1 net: ppp: fix creating PPP pass and active filters

From: Christoph Schulz <[email protected]>

Commit 568f194e8bd16c353ad50f9ab95d98b20578a39d ("net: ppp: use sk_unattached_filter api") inadvertently changed the logic when setting PPP pass and active filters. This applies to both the generic PPP subsystem implemented by drivers/net/ppp/ppp_generic.c and the ISDN PPP subsystem implemented by drivers/isdn/i4l/isdn_ppp.c. The original code in ppp_ioctl() (or isdn_ppp_ioctl(), resp.) handling PPPIOCSPASS and PPPIOCSACTIVE allowed to remove a pass/active filter previously set by using a filter of length zero. However, with the new code this is not possible anymore as this case is not explicitly checked for, which leads to passing NULL as a filter to sk_unattached_filter_create(). This results in returning EINVAL to the caller.

Additionally, the variables ppp->pass_filter and ppp->active_filter (or is->pass_filter and is->active_filter, resp.) are not reset to NULL, although the filters they point to may have been destroyed by sk_unattached_filter_destroy(), so in this EINVAL case dangling pointers are left behind (provided the pointers were previously non-NULL).

This patch corrects both problems by checking whether the filter passed is empty or non-empty, and prevents sk_unattached_filter_create() from being called in the first case. Moreover, the pointers are always reset to NULL as soon as sk_unattached_filter_destroy() returns.

Signed-off-by Christoph Schulz <[email protected]>

---

drivers/isdn/i4l/isdn_ppp.c +16 -4

index 61ac632..cd2f4c3 100644
@@ -644,9 +644,15 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
 		fprog.len = len;
 		fprog.filter = code;
 
-		if (is->pass_filter)
+		if (is->pass_filter) {
 			sk_unattached_filter_destroy(is->pass_filter);
-		err = sk_unattached_filter_create(&is->pass_filter, &fprog);
+			is->pass_filter = NULL;
+		}
+		if (fprog.filter != NULL)
+			err = sk_unattached_filter_create(&is->pass_filter,
+							  &fprog);
+		else
+			err = 0;
 		kfree(code);
 
 		return err;

@@ -663,9 +669,15 @@ isdn_ppp_ioctl(int min, struct file *file, unsigned int cmd, unsigned long arg)
 		fprog.len = len;
 		fprog.filter = code;
 
-		if (is->active_filter)
+		if (is->active_filter) {
 			sk_unattached_filter_destroy(is->active_filter);
-		err = sk_unattached_filter_create(&is->active_filter, &fprog);
+			is->active_filter = NULL;
+		}
+		if (fprog.filter != NULL)
+			err = sk_unattached_filter_create(&is->active_filter,
+							  &fprog);
+		else
+			err = 0;
 		kfree(code);
 
 		return err;

drivers/net/ppp/ppp_generic.c +16 -6

index 91d6c12..d0f6f93 100644
@@ -763,10 +763,15 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			};
 
 			ppp_lock(ppp);
-			if (ppp->pass_filter)
+			if (ppp->pass_filter) {
 				sk_unattached_filter_destroy(ppp->pass_filter);
-			err = sk_unattached_filter_create(&ppp->pass_filter,
-							  &fprog);
+				ppp->pass_filter = NULL;
+			}
+			if (fprog.filter != NULL)
+				err = sk_unattached_filter_create(&ppp->pass_filter,
+								  &fprog);
+			else
+				err = 0;
 			kfree(code);
 			ppp_unlock(ppp);
 		}

@@ -784,10 +789,15 @@ static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 			};
 
 			ppp_lock(ppp);
-			if (ppp->active_filter)
+			if (ppp->active_filter) {
 				sk_unattached_filter_destroy(ppp->active_filter);
-			err = sk_unattached_filter_create(&ppp->active_filter,
-							  &fprog);
+				ppp->active_filter = NULL;
+			}
+			if (fprog.filter != NULL)
+				err = sk_unattached_filter_create(&ppp->active_filter,
+								  &fprog);
+			else
+				err = 0;
 			kfree(code);
 			ppp_unlock(ppp);
 		}

David Miller

maintainer

2014-07-17 06:42 UTC #1 lore raw

From: Christoph Schulz <[email protected]>
Date: Wed, 16 Jul 2014 22:10:29 +0200

Quoted 19 lines

From: Christoph Schulz <[email protected]>
Commit 568f194e8bd16c353ad50f9ab95d98b20578a39d ("net: ppp: use sk_unattached_filter api") inadvertently changed the logic when setting PPP pass and active filters. This applies to both the generic PPP subsystem implemented by drivers/net/ppp/ppp_generic.c and the ISDN PPP subsystem implemented by drivers/isdn/i4l/isdn_ppp.c. The original code in ppp_ioctl() (or isdn_ppp_ioctl(), resp.) handling PPPIOCSPASS and PPPIOCSACTIVE allowed to remove a pass/active filter previously set by using a filter of length zero. However, with the new code this is not possible anymore as this case is not explicitly checked for, which leads to passing NULL as a filter to sk_unattached_filter_create(). This results in returning EINVAL to the caller.
Additionally, the variables ppp->pass_filter and ppp->active_filter (or is->pass_filter and is->active_filter, resp.) are not reset to NULL, although the filters they point to may have been destroyed by sk_unattached_filter_destroy(), so in this EINVAL case dangling pointers are left behind (provided the pointers were previously non-NULL).

Quoted 6 lines

This patch corrects both problems by checking whether the filter passed is empty or non-empty, and prevents sk_unattached_filter_create() from being called in the first case. Moreover, the pointers are always reset to NULL as soon as sk_unattached_filter_destroy() returns.
Signed-off-by Christoph Schulz <[email protected]>

Applied and queued up for -stable, thanks.