[PATCH] landlock: shrink tsync works[] on partial allocation failure

[Peng Hao]

When the per-slot kzalloc fails mid-loop in tsync_works_grow_by(), the
already-enlarged s->works array keeps uninitialized trailing entries.
Shrink the array back to its used size on the error path so no waste
is carried over: free it outright when nothing has been allocated yet,
otherwise try a shrinking krealloc_array() (keep the larger array if
the shrink fails, since tsync_works_release() honors s->capacity).

Signed-off-by: Peng Hao <flyingpeng at tencent.com>
---
 security/landlock/tsync.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/security/landlock/tsync.c b/security/landlock/tsync.c
index c5730bbd..356ce94b 100644
--- a/security/landlock/tsync.c
+++ b/security/landlock/tsync.c
@@ -272,9 +272,23 @@ static int tsync_works_grow_by(struct tsync_works *s, size_t n, gfp_t flags)
 		work = kzalloc_obj(*work, flags);
 		if (!work) {
 			/*
-			 * Leave the object in a consistent state,
-			 * but return an error.
+			 * Leave the object in a consistent state, but return
+			 * an error.  Shrink @s->works back to its used size to
+			 * avoid carrying uninitialized trailing entries.  A
+			 * shrinking krealloc_array() should normally succeed,
+			 * but if it does not we simply keep the larger array;
+			 * tsync_works_release() iterates only up to capacity.
 			 */
+			if (i == 0) {
+				kfree(s->works);
+				s->works = NULL;
+			} else {
+				works = krealloc_array(s->works, i,
+						       sizeof(s->works[0]),
+						       flags | __GFP_NOWARN);
+				if (works)
+					s->works = works;
+			}
 			s->capacity = i;
 			return -ENOMEM;
 		}
-- 
2.43.7