[RFC PATCH v6 27/34] dyndbg: fixup protect header when deleting site

Jim Cromie
2021-05-29T20:03:41Z

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 659e864837ad..f2f6f2b20d01 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