[syzbot] [net?] memory leak in xfrm_policy_construct

[syzbot] [net?] memory leak in xfrm_policy_construct

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    a0c83177734a Merge tag 'drm-fixes-2026-03-21' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=117d66da580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e2bba615ee79faa5
dashboard link: https://syzkaller.appspot.com/bug?extid=901d48e0b95aed4a2548
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12a481d6580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1669ccba580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/76025f732b88/disk-a0c83177.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/51c8f0f97de7/vmlinux-a0c83177.xz
kernel image: https://storage.googleapis.com/syzbot-assets/46b7135c73d1/bzImage-a0c83177.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+901d48e0b95aed4a2548@syzkaller.appspotmail.com

2026/03/21 23:24:08 executed programs: 5
BUG: memory leak
unreferenced object 0xffff888125a86c00 (size 1024):
  comm "syz.0.17", pid 6082, jiffies 4294946151
  hex dump (first 32 bytes):
    00 e5 5f 1c 81 88 ff ff 00 00 00 00 00 00 00 00  .._.............
    22 01 00 00 00 00 ad de 00 01 00 00 00 00 ad de  "...............
  backtrace (crc f62518df):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4543 [inline]
    slab_alloc_node mm/slub.c:4866 [inline]
    __kmalloc_cache_noprof+0x377/0x480 mm/slub.c:5375
    kmalloc_noprof include/linux/slab.h:950 [inline]
    kzalloc_noprof include/linux/slab.h:1188 [inline]
    xfrm_policy_alloc+0x63/0x180 net/xfrm/xfrm_policy.c:432
    xfrm_policy_construct+0x30/0x260 net/xfrm/xfrm_user.c:2187
    xfrm_add_policy+0x12e/0x390 net/xfrm/xfrm_user.c:2246
    xfrm_user_rcv_msg+0x248/0x570 net/xfrm/xfrm_user.c:3507
    netlink_rcv_skb+0x89/0x1c0 net/netlink/af_netlink.c:2550
    xfrm_netlink_rcv+0x34/0x40 net/xfrm/xfrm_user.c:3529
    netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
    netlink_unicast+0x3a1/0x4f0 net/netlink/af_netlink.c:1344
    netlink_sendmsg+0x335/0x690 net/netlink/af_netlink.c:1894
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    ____sys_sendmsg+0x54a/0x580 net/socket.c:2592
    ___sys_sendmsg+0x101/0x140 net/socket.c:2646
    __sys_sendmsg+0xcd/0x140 net/socket.c:2678
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF


---
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Forwarded: [PATCH] xfrm: fix memory leak and improper cleanup in xfrm_add_policy()

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] xfrm: fix memory leak and improper cleanup in xfrm_add_policy()
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


When xfrm_policy_insert() fails in xfrm_add_policy(), the error
handling path manually calls xfrm_dev_policy_free(), followed by
security_xfrm_policy_free() and a raw kfree(). This is problematic
for three reasons:

1. xfrm_policy_destroy() already calls xfrm_dev_policy_free()
   internally, so the manual call results in a double-free.

2. xfrm_policy_destroy() frees the policy asynchronously via
   call_rcu(), which schedules xfrm_policy_destroy_rcu() to call
   security_xfrm_policy_free() and kfree(). The manual
   security_xfrm_policy_free() call before kfree() races with this
   RCU callback, causing another double-free.

3. The raw kfree() is not RCU-safe and may free memory that is still
   being accessed by concurrent RCU readers.

Fix this by using xfrm_policy_destroy() as the single, correct
cleanup path, consistent with how xfrm_policy_construct() handles
its own error paths. The walk.dead flag must be set first as
xfrm_policy_destroy() requires it via BUG_ON(!policy->walk.dead).

Reported-by: syzbot+901d48e0b95aed4a2548@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=901d48e0b95aed4a2548
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 net/xfrm/xfrm_user.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index d56450f61669..ae144d1e4a65 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2267,9 +2267,8 @@ static int xfrm_add_policy(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 	if (err) {
 		xfrm_dev_policy_delete(xp);
-		xfrm_dev_policy_free(xp);
-		security_xfrm_policy_free(xp->security);
-		kfree(xp);
+		xp->walk.dead = 1;
+		xfrm_policy_destroy(xp);
 		return err;
 	}
 
-- 
2.43.0

Re: [syzbot] [net?] memory leak in xfrm_policy_construct

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+901d48e0b95aed4a2548@syzkaller.appspotmail.com
Tested-by: syzbot+901d48e0b95aed4a2548@syzkaller.appspotmail.com

Tested on:

commit:         f5459048 Merge tag 'i2c-for-7.0-final' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12b8f302580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e2bba615ee79faa5
dashboard link: https://syzkaller.appspot.com/bug?extid=901d48e0b95aed4a2548
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=14e2c74e580000

Note: testing is done by a robot and is best-effort only.