linux-kernel - [PATCH] radix tree: fix kmemleak false positive in radix_tree

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250514180137.363929-1-jkangas@redhat.com>
Date: Wed, 14 May 2025 11:01:37 -0700
From: Jared Kangas <jkangas@...hat.com>
To: willy@...radead.org,
	akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,
	Jared Kangas <jkangas@...hat.com>
Subject: [PATCH] radix tree: fix kmemleak false positive in radix_tree_shrink()

Kmemleak periodically produces a false positive report that resembles
the following:

unreferenced object 0xffff00000db613b8 (size 576):
  comm "systemd", pid 1, jiffies 4294987015
  hex dump (first 32 bytes):
    00 22 01 00 00 00 00 00 28 1c d5 c5 00 00 ff ff  ."......(.......
    10 e4 6c c0 00 00 ff ff d0 13 b6 0d 00 00 ff ff  ..l.............
  backtrace (crc 520d6e1c):
    kmemleak_alloc+0xb4/0xc4
    kmem_cache_alloc+0x288/0x2b0
    radix_tree_node_alloc.constprop.0+0x214/0x364
    idr_get_free+0x3d0/0x690
    idr_alloc_u32+0x120/0x280
    idr_alloc_cyclic+0xe8/0x1b4
    __kernfs_new_node+0x118/0x5a0
    kernfs_create_dir_ns+0x8c/0x1fc
    cgroup_create+0x1cc/0x8a0
    cgroup_mkdir+0x13c/0x90c
    kernfs_iop_mkdir+0x108/0x184
    vfs_mkdir+0x3c8/0x5f0
    do_mkdirat+0x218/0x290
    __arm64_sys_mkdirat+0xe0/0x140
    invoke_syscall.constprop.0+0x74/0x1e4
    do_el0_svc+0xd0/0x1dc

This is a transient leak that can be traced to radix_tree_shrink(): when
root->xa_head is set, kmemleak may have already started traversing the
radix tree. If this has happened, but kmemleak fails to scan the new
xa_head before it moves, kmemleak will see it as a leak until the radix
tree is scanned again.

Mark the new xa_head as a transient leak to prevent this false positive
report.

Signed-off-by: Jared Kangas <jkangas@...hat.com>
---
 lib/radix-tree.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 976b9bd02a1b5..79b3702a0cb54 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -509,6 +509,14 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root)
 		if (is_idr(root) && !tag_get(node, IDR_FREE, 0))
 			root_tag_clear(root, IDR_FREE);
 
+		/*
+		 * Kmemleak might report a false positive if it traverses the
+		 * tree while we're shrinking it, since the reference moves
+		 * from node->slots[0] to root->xa_head.
+		 */
+		if (radix_tree_is_internal_node(child))
+			kmemleak_transient_leak(entry_to_node(child));
+
 		/*
 		 * We have a dilemma here. The node's slot[0] must not be
 		 * NULLed in case there are concurrent lookups expecting to
-- 
2.49.0