[RFC PATCH v5 26/28] dyndbg: fixup protect header when deleting site

From: Jim Cromie <jim.cromie@gmail.com>
To: Jason Baron <jbaron@akamai.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, Jim Cromie <jim.cromie@gmail.com>
Subject: [RFC PATCH v5 26/28] dyndbg: fixup protect header when deleting site
Date: Tue, 11 May 2021 12:50:55 -0600	[thread overview]
Message-ID: <20210511185057.3815777-27-jim.cromie@gmail.com> (raw)
In-Reply-To: <20210511185057.3815777-1-jim.cromie@gmail.com>

fix a null-ptr-deref when .site info is deleted.

 #> echo +D > /proc/dynamic_debug/control

This protects the header.site pointer from zeroing; we need it for all
the SITE_CHK sanity checking.  Probably should protect against
toggling the static_key too (in the same function), but this smaller
change fixes the crash.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 lib/dynamic_debug.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index b61e4a211819..aa4a476d70ad 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -247,7 +247,7 @@ static void ddebug_alter_site(struct _ddebug *dp,
 #ifdef SITE_CHK
 	/* delete site info for this callsite */
 	if (modifiers->flags & _DPRINTK_FLAGS_DELETE_SITE) {
-		if (dp->site) {
+		if (dp->site && !is_dyndbg_header_pair(dp, dp->site)) {
 			vpr_info("dropping site info %s.%s.%d\n", dp->site->filename,
 				dp->site->function, dp->lineno);
 			dp->site = NULL;
-- 
2.31.1

