From: Geliang Tang Date: Tue, 21 Jul 2026 22:14:39 +0000 (+0200) Subject: mptcp: pm: userspace: fix use-after-free in get_local_id X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=9bc6d5e4ca9f3cbb41d43400b3a31cb0403796c9;p=thirdparty%2Fkernel%2Flinux.git mptcp: pm: userspace: fix use-after-free in get_local_id In mptcp_pm_userspace_get_local_id(), the address entry is looked up under spinlock, but its id is read after dropping the lock. A concurrent deletion can free the entry between the unlock and the read, leading to UAF. The race window is narrow. It was reproduced only with a locally constructed stress test that repeatedly overlaps an MP_JOIN SYN with a MPTCP_PM_CMD_SUBFLOW_DESTROY request. However, the KASAN report below confirms that the race is reachable: [ 666.319376] BUG: KASAN: slab-use-after-free in mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319386] Read of size 1 at addr ffff888124845610 by task swapper/0/0 ... [ 666.319401] Call Trace: [ 666.319405] [ 666.319408] dump_stack_lvl+0x53/0x70 [ 666.319412] print_address_description.constprop.0+0x2c/0x3b0 [ 666.319418] print_report+0xbe/0x2b0 [ 666.319421] ? mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319423] kasan_report+0xce/0x100 [ 666.319426] ? mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319429] mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319433] mptcp_pm_get_local_id+0x371/0x440 ... [ 666.319821] Allocated by task 45539: [ 666.319844] kasan_save_stack+0x33/0x60 [ 666.319855] kasan_save_track+0x14/0x30 [ 666.319858] __kasan_kmalloc+0x8f/0xa0 [ 666.319863] __kmalloc_noprof+0x1e7/0x520 [ 666.319867] sock_kmalloc+0xdf/0x130 [ 666.319885] sock_kmemdup+0x1b/0x40 [ 666.319888] mptcp_userspace_pm_append_new_local_addr+0x261/0x500 [ 666.319910] mptcp_pm_nl_announce_doit+0x16a/0x610 ... [ 666.319967] Freed by task 45560: [ 666.319988] kasan_save_stack+0x33/0x60 [ 666.319991] kasan_save_track+0x14/0x30 [ 666.319994] kasan_save_free_info+0x3b/0x60 [ 666.319998] __kasan_slab_free+0x43/0x70 [ 666.320000] kfree+0x166/0x440 [ 666.320003] sock_kfree_s+0x1d/0x50 [ 666.320007] mptcp_userspace_pm_delete_local_addr.isra.0+0x157/0x200 [ 666.320011] mptcp_pm_nl_subflow_destroy_doit+0x51d/0xea0 Fix by copying the id into a local variable while still holding the lock, and use -1 as a "not found" sentinel. Fixes: f012d796a6de ("mptcp: check addrs list in userspace_pm_get_local_id") Cc: stable@vger.kernel.org Signed-off-by: Geliang Tang Tested-by: Xuanqiang Luo Reviewed-by: Matthieu Baerts (NGI0) Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260722-net-mptcp-misc-fixes-7-2-rc5-v1-2-6fb595bc86ef@kernel.org Signed-off-by: Jakub Kicinski --- diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c index d100867e9202..945aa5afc2dd 100644 --- a/net/mptcp/pm_userspace.c +++ b/net/mptcp/pm_userspace.c @@ -132,12 +132,15 @@ int mptcp_userspace_pm_get_local_id(struct mptcp_sock *msk, __be16 msk_sport = ((struct inet_sock *) inet_sk((struct sock *)msk))->inet_sport; struct mptcp_pm_addr_entry *entry; + int id; spin_lock_bh(&msk->pm.lock); entry = mptcp_userspace_pm_lookup_addr(msk, &skc->addr); + id = entry ? entry->addr.id : -1; spin_unlock_bh(&msk->pm.lock); - if (entry) - return entry->addr.id; + + if (id != -1) + return id; if (skc->addr.port == msk_sport) skc->addr.port = 0;