6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet edumazet@google.com
[ Upstream commit d13a3824bfd2b4774b671a75cf766a16637a0e67 ]
syzbot found its way in net/atm/lec.c, and found an error path in lecd_attach() could leave a dangling pointer in dev_lec[].
Add a mutex to protect dev_lecp[] uses from lecd_attach(), lec_vcc_attach() and lec_mcast_attach().
Following patch will use this mutex for /proc/net/atm/lec.
BUG: KASAN: slab-use-after-free in lecd_attach net/atm/lec.c:751 [inline] BUG: KASAN: slab-use-after-free in lane_ioctl+0x2224/0x23e0 net/atm/lec.c:1008 Read of size 8 at addr ffff88807c7b8e68 by task syz.1.17/6142
CPU: 1 UID: 0 PID: 6142 Comm: syz.1.17 Not tainted 6.16.0-rc1-syzkaller-00239-g08215f5486ec #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xcd/0x680 mm/kasan/report.c:521 kasan_report+0xe0/0x110 mm/kasan/report.c:634 lecd_attach net/atm/lec.c:751 [inline] lane_ioctl+0x2224/0x23e0 net/atm/lec.c:1008 do_vcc_ioctl+0x12c/0x930 net/atm/ioctl.c:159 sock_do_ioctl+0x118/0x280 net/socket.c:1190 sock_ioctl+0x227/0x6b0 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK>
Allocated by task 6132: kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 kasan_save_track+0x14/0x30 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:377 [inline] __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394 kasan_kmalloc include/linux/kasan.h:260 [inline] __do_kmalloc_node mm/slub.c:4328 [inline] __kvmalloc_node_noprof+0x27b/0x620 mm/slub.c:5015 alloc_netdev_mqs+0xd2/0x1570 net/core/dev.c:11711 lecd_attach net/atm/lec.c:737 [inline] lane_ioctl+0x17db/0x23e0 net/atm/lec.c:1008 do_vcc_ioctl+0x12c/0x930 net/atm/ioctl.c:159 sock_do_ioctl+0x118/0x280 net/socket.c:1190 sock_ioctl+0x227/0x6b0 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 6132: kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 kasan_save_track+0x14/0x30 mm/kasan/common.c:68 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576 poison_slab_object mm/kasan/common.c:247 [inline] __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264 kasan_slab_free include/linux/kasan.h:233 [inline] slab_free_hook mm/slub.c:2381 [inline] slab_free mm/slub.c:4643 [inline] kfree+0x2b4/0x4d0 mm/slub.c:4842 free_netdev+0x6c5/0x910 net/core/dev.c:11892 lecd_attach net/atm/lec.c:744 [inline] lane_ioctl+0x1ce8/0x23e0 net/atm/lec.c:1008 do_vcc_ioctl+0x12c/0x930 net/atm/ioctl.c:159 sock_do_ioctl+0x118/0x280 net/socket.c:1190 sock_ioctl+0x227/0x6b0 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+8b64dec3affaed7b3af5@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6852c6f6.050a0220.216029.0018.GAE@google.com/... Signed-off-by: Eric Dumazet edumazet@google.com Link: https://patch.msgid.link/20250618140844.1686882-2-edumazet@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/atm/lec.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/net/atm/lec.c b/net/atm/lec.c index ac3cfc1ae5102..d4ac1488eca6f 100644 --- a/net/atm/lec.c +++ b/net/atm/lec.c @@ -124,6 +124,7 @@ static unsigned char bus_mac[ETH_ALEN] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
/* Device structures */ static struct net_device *dev_lec[MAX_LEC_ITF]; +static DEFINE_MUTEX(lec_mutex);
#if IS_ENABLED(CONFIG_BRIDGE) static void lec_handle_bridge(struct sk_buff *skb, struct net_device *dev) @@ -685,6 +686,7 @@ static int lec_vcc_attach(struct atm_vcc *vcc, void __user *arg) int bytes_left; struct atmlec_ioc ioc_data;
+ lockdep_assert_held(&lec_mutex); /* Lecd must be up in this case */ bytes_left = copy_from_user(&ioc_data, arg, sizeof(struct atmlec_ioc)); if (bytes_left != 0) @@ -710,6 +712,7 @@ static int lec_vcc_attach(struct atm_vcc *vcc, void __user *arg)
static int lec_mcast_attach(struct atm_vcc *vcc, int arg) { + lockdep_assert_held(&lec_mutex); if (arg < 0 || arg >= MAX_LEC_ITF) return -EINVAL; arg = array_index_nospec(arg, MAX_LEC_ITF); @@ -725,6 +728,7 @@ static int lecd_attach(struct atm_vcc *vcc, int arg) int i; struct lec_priv *priv;
+ lockdep_assert_held(&lec_mutex); if (arg < 0) arg = 0; if (arg >= MAX_LEC_ITF) @@ -742,6 +746,7 @@ static int lecd_attach(struct atm_vcc *vcc, int arg) snprintf(dev_lec[i]->name, IFNAMSIZ, "lec%d", i); if (register_netdev(dev_lec[i])) { free_netdev(dev_lec[i]); + dev_lec[i] = NULL; return -EINVAL; }
@@ -1003,6 +1008,7 @@ static int lane_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg) return -ENOIOCTLCMD; }
+ mutex_lock(&lec_mutex); switch (cmd) { case ATMLEC_CTRL: err = lecd_attach(vcc, (int)arg); @@ -1017,6 +1023,7 @@ static int lane_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg) break; }
+ mutex_unlock(&lec_mutex); return err; }