[syzbot] [nfs?] memory leak in percpu_ref_init

[syzbot] [nfs?] memory leak in percpu_ref_init

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    d358e5254674 Merge tag 'for-6.19/dm-changes' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176f561a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9a0268003e02068d
dashboard link: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15a6661a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d4a1b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e79f317bb571/disk-d358e525.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cf9e2849af10/vmlinux-d358e525.xz
kernel image: https://storage.googleapis.com/syzbot-assets/73d80a967038/bzImage-d358e525.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com

BUG: memory leak
unreferenced object (percpu) 0x607e4d6bd360 (size 8):
  comm "syz.0.17", pid 6093, jiffies 4294942369
  hex dump (first 8 bytes on cpu 0):
    00 00 00 00 00 00 00 00                          ........
  backtrace (crc 0):
    pcpu_alloc_noprof+0x82c/0xd60 mm/percpu.c:1890
    percpu_ref_init+0x36/0x1e0 lib/percpu-refcount.c:72
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    netlink_rcv_skb+0x93/0x1d0 net/netlink/af_netlink.c:2550
    genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
    netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
    netlink_unicast+0x3a3/0x4f0 net/netlink/af_netlink.c:1344
    netlink_sendmsg+0x335/0x6b0 net/netlink/af_netlink.c:1894
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    ____sys_sendmsg+0x562/0x5a0 net/socket.c:2592
    ___sys_sendmsg+0xc8/0x130 net/socket.c:2646
    __sys_sendmsg+0xc7/0x140 net/socket.c:2678
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff88812a39dfc0 (size 64):
  comm "syz.0.17", pid 6093, jiffies 4294942369
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 80 80 59 d7 81 ff ff ff ff  .........Y......
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc a2262fc6):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    __kmalloc_cache_noprof+0x3b2/0x570 mm/slub.c:5771
    kmalloc_noprof include/linux/slab.h:957 [inline]
    kzalloc_noprof include/linux/slab.h:1094 [inline]
    percpu_ref_init+0x94/0x1e0 lib/percpu-refcount.c:76
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    netlink_rcv_skb+0x93/0x1d0 net/netlink/af_netlink.c:2550
    genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
    netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
    netlink_unicast+0x3a3/0x4f0 net/netlink/af_netlink.c:1344
    netlink_sendmsg+0x335/0x6b0 net/netlink/af_netlink.c:1894
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    ____sys_sendmsg+0x562/0x5a0 net/socket.c:2592
    ___sys_sendmsg+0xc8/0x130 net/socket.c:2646
    __sys_sendmsg+0xc7/0x140 net/socket.c:2678
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object (percpu) 0x607e4d6bd368 (size 8):
  comm "syz.0.18", pid 6095, jiffies 4294942370
  hex dump (first 8 bytes on cpu 0):
    00 00 00 00 00 00 00 00                          ........
  backtrace (crc 0):
    pcpu_alloc_noprof+0x82c/0xd60 mm/percpu.c:1890
    percpu_ref_init+0x36/0x1e0 lib/percpu-refcount.c:72
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    netlink_rcv_skb+0x93/0x1d0 net/netlink/af_netlink.c:2550
    genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
    netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
    netlink_unicast+0x3a3/0x4f0 net/netlink/af_netlink.c:1344
    netlink_sendmsg+0x335/0x6b0 net/netlink/af_netlink.c:1894
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    ____sys_sendmsg+0x562/0x5a0 net/socket.c:2592
    ___sys_sendmsg+0xc8/0x130 net/socket.c:2646
    __sys_sendmsg+0xc7/0x140 net/socket.c:2678
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

BUG: memory leak
unreferenced object 0xffff88812833c840 (size 64):
  comm "syz.0.18", pid 6095, jiffies 4294942370
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 80 80 59 d7 81 ff ff ff ff  .........Y......
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc a2262fc6):
    kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
    slab_post_alloc_hook mm/slub.c:4958 [inline]
    slab_alloc_node mm/slub.c:5263 [inline]
    __kmalloc_cache_noprof+0x3b2/0x570 mm/slub.c:5771
    kmalloc_noprof include/linux/slab.h:957 [inline]
    kzalloc_noprof include/linux/slab.h:1094 [inline]
    percpu_ref_init+0x94/0x1e0 lib/percpu-refcount.c:76
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    netlink_rcv_skb+0x93/0x1d0 net/netlink/af_netlink.c:2550
    genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
    netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
    netlink_unicast+0x3a3/0x4f0 net/netlink/af_netlink.c:1344
    netlink_sendmsg+0x335/0x6b0 net/netlink/af_netlink.c:1894
    sock_sendmsg_nosec net/socket.c:727 [inline]
    __sock_sendmsg net/socket.c:742 [inline]
    ____sys_sendmsg+0x562/0x5a0 net/socket.c:2592
    ___sys_sendmsg+0xc8/0x130 net/socket.c:2646
    __sys_sendmsg+0xc7/0x140 net/socket.c:2678
    do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
    do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94
    entry_SYSCALL_64_after_hwframe+0x77/0x7f

connection error: failed to recv *flatrpc.ExecutorMessageRawT: read tcp 127.0.0.1:36571->127.0.0.1:45172: read: connection reset by peer


---
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Forwarded: [PATCH] nfsd: fix memory leak in nfsd_create_serv error paths

[syzbot]

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

***

Subject: [PATCH] nfsd: fix memory leak in nfsd_create_serv error paths
Author: kartikey406@gmail.com

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

When svc_create_pooled() or svc_bind() fails, nfsd_create_serv() returns
an error without calling percpu_ref_exit() to clean up the percpu
reference that was initialized earlier in the function.

This causes two memory leaks per failed call:
  - 8 bytes of percpu memory (the reference counter)
  - 64 bytes of slab memory (the percpu_ref_data structure)

Fix this by adding an error label that calls percpu_ref_exit() before
returning.

Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/nfsd/nfssvc.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b08ae85d53ef..49fd77c8f98d 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -615,13 +615,14 @@ int nfsd_create_serv(struct net *net)
 	serv = svc_create_pooled(nfsd_programs, ARRAY_SIZE(nfsd_programs),
 				 &nn->nfsd_svcstats,
 				 nfsd_max_blksize, nfsd);
-	if (serv == NULL)
-		return -ENOMEM;
-
+	if (serv == NULL) {
+		error = -ENOMEM;
+		goto err_percpu;
+	}
 	error = svc_bind(serv, net);
 	if (error < 0) {
 		svc_destroy(&serv);
-		return error;
+		goto err_percpu;
 	}
 	spin_lock(&nfsd_notifier_lock);
 	nn->nfsd_serv = serv;
@@ -636,6 +637,9 @@ int nfsd_create_serv(struct net *net)
 	}
 	nfsd_reset_write_verifier(nn);
 	return 0;
+err_percpu:
+	percpu_ref_exit(&nn->nfsd_net_ref);
+	return error;
 }
 
 int nfsd_nrpools(struct net *net)
-- 
2.43.0

Forwarded: [PATCH] nfsd: fix percpu_ref leak when nfsd_net_up is false

[syzbot]

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

***

Subject: [PATCH] nfsd: fix percpu_ref leak when nfsd_net_up is false
Author: kartikey406@gmail.com

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

When nfsd_destroy_serv() is called without any threads being started,
nfsd_startup_net() was never invoked, so nfsd_net_up remains false.

In this case, nfsd_shutdown_net() returns early without calling
percpu_ref_exit() to free the percpu reference initialized in
nfsd_create_serv().

This causes two memory leaks per call:
  - 8 bytes of percpu memory (the reference counter)
  - 64 bytes of slab memory (the percpu_ref_data structure)

Fix this by calling percpu_ref_exit() in the early return path when
nfsd_net_up is false.

Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
Fixes: 47e988147f40 ("nfsd: add nfsd_serv_try_get and nfsd_serv_put")
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/nfsd/nfssvc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b08ae85d53ef..00c6a0c96885 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -406,8 +406,10 @@ static void nfsd_shutdown_net(struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	if (!nn->nfsd_net_up)
+	if (!nn->nfsd_net_up) {
+		percpu_ref_exit(&nn->nfsd_net_ref);
 		return;
+	}
 
 	percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
 	wait_for_completion(&nn->nfsd_net_confirm_done);
-- 
2.43.0

[PATCH] NFSD: net ref data still needs to be freed even if net hasn't startup

[Edward Adam Davis]

When the NFSD instance doesn't to startup, the net ref data memory is
not properly reclaimed, which triggers the memory leak issue reported
by syzbot [1].

To avoid the problem reported in [1], the net ref data memory reclamation
action is moved outside of nfsd_net_up when the net is shutdown.

[1]
BUG: memory leak
unreferenced object 0xffff88812a39dfc0 (size 64):
  backtrace (crc a2262fc6):
    percpu_ref_init+0x94/0x1e0 lib/percpu-refcount.c:76
    nfsd_create_serv+0xbe/0x260 fs/nfsd/nfssvc.c:605
    nfsd_nl_listener_set_doit+0x62/0xb00 fs/nfsd/nfsctl.c:1882
    genl_family_rcv_msg_doit+0x11e/0x190 net/netlink/genetlink.c:1115
    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
    genl_rcv_msg+0x2fd/0x440 net/netlink/genetlink.c:1210
    
Reported-by: syzbot+6ee3b889bdeada0a6226@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6ee3b889bdeada0a6226
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/nfsd/nfssvc.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b08ae85d53ef..e2b2cf0dd013 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -406,26 +406,26 @@ static void nfsd_shutdown_net(struct net *net)
 {
 	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
 
-	if (!nn->nfsd_net_up)
-		return;
-
-	percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
-	wait_for_completion(&nn->nfsd_net_confirm_done);
-
-	nfsd_export_flush(net);
-	nfs4_state_shutdown_net(net);
-	nfsd_reply_cache_shutdown(nn);
-	nfsd_file_cache_shutdown_net(net);
-	if (nn->lockd_up) {
-		lockd_down(net);
-		nn->lockd_up = false;
+	if (nn->nfsd_net_up) {
+		percpu_ref_kill_and_confirm(&nn->nfsd_net_ref, nfsd_net_done);
+		wait_for_completion(&nn->nfsd_net_confirm_done);
+
+		nfsd_export_flush(net);
+		nfs4_state_shutdown_net(net);
+		nfsd_reply_cache_shutdown(nn);
+		nfsd_file_cache_shutdown_net(net);
+		if (nn->lockd_up) {
+			lockd_down(net);
+			nn->lockd_up = false;
+		}
+		wait_for_completion(&nn->nfsd_net_free_done);
 	}
 
-	wait_for_completion(&nn->nfsd_net_free_done);
 	percpu_ref_exit(&nn->nfsd_net_ref);
 
+	if (nn->nfsd_net_up)
+		nfsd_shutdown_generic();
 	nn->nfsd_net_up = false;
-	nfsd_shutdown_generic();
 }
 
 static DEFINE_SPINLOCK(nfsd_notifier_lock);
-- 
2.43.0

Re: [PATCH] NFSD: net ref data still needs to be freed even if net hasn't startup

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

On Tue, 16 Dec 2025 18:27:37 +0800, Edward Adam Davis wrote:
> When the NFSD instance doesn't to startup, the net ref data memory is
> not properly reclaimed, which triggers the memory leak issue reported
> by syzbot [1].
> 
> To avoid the problem reported in [1], the net ref data memory reclamation
> action is moved outside of nfsd_net_up when the net is shutdown.
> 
> [...]

Applied to nfsd-testing, thanks!

[1/1] NFSD: net ref data still needs to be freed even if net hasn't startup
      commit: 339bafeb9942cb3f42c34ed5fcf1fbe377a492da

--
Chuck Lever