From: Eric Dumazet <edumazet@google.com> mainline inclusion from mainline-v7.2-rc3 commit 7b19c0f81ed1fdaec6bc522569be367199a9edf3 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/9704 CVE: CVE-2026-72323 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- A race condition exists between device teardown (inetdev_destroy) and incoming IGMP query processing (igmp_rcv), leading to a Use-After-Free in the IGMP timer callback. During device destruction, inetdev_destroy() drops the primary reference to in_device, which can drop its refcount to 0. The actual freeing of in_device memory is deferred via RCU (using call_rcu()). Concurrently, igmp_rcv() runs under RCU read lock and obtains the in_device pointer. Because the memory is RCU-protected, CPU-0 can safely dereference in_device even if its refcount has hit 0. However, if CPU-0 calls igmp_gq_start_timer() and re-arms the timer, it attempts to acquire a reference using in_dev_hold(). This increments the refcount from 0 to 1, triggering a "refcount_t: addition on 0" warning. Since the in_device memory is still scheduled to be freed after the RCU grace period (as the free callback does not check the refcount again), the device is freed while the timer is still armed. When the timer expires, it accesses the freed memory, causing a kernel panic. Fix this by using refcount_inc_not_zero() (via a new helper in_dev_hold_safe()) to prevent acquiring a reference if the device is already being destroyed. If the refcount is 0, we do not arm the timer. A similar issue in IPv6 MLD is fixed in a subsequent patch. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: Zero Day Initiative <zdi-disclosures@trendmicro.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com> Link: https://patch.msgid.link/20260705181756.963063-2-edumazet@google.com Signed-off-by: Paolo Abeni <pabeni@redhat.com> Conflicts: net/ipv4/igmp.c [For 4.19, get_random_u32_below() is not available, so igmp_ifc_start_timer() retains the original prandom_u32() % delay approach. The remaining refcount logic and the newly added in_dev_hold_safe() parts are consistent with upstream.] Signed-off-by: JiangJieHua <jiangjiehua1@huawei.com> --- include/linux/inetdevice.h | 5 +++++ net/ipv4/igmp.c | 14 +++++++++----- 2 files changed, 14 insertions(+), 5 deletions(-) diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h index a64f21a97369a..002f1de9a30f4 100644 --- a/include/linux/inetdevice.h +++ b/include/linux/inetdevice.h @@ -255,6 +255,11 @@ static inline void in_dev_put(struct in_device *idev) #define __in_dev_put(idev) refcount_dec(&(idev)->refcnt) #define in_dev_hold(idev) refcount_inc(&(idev)->refcnt) +static inline bool in_dev_hold_safe(struct in_device *idev) +{ + return refcount_inc_not_zero(&idev->refcnt); +} + #endif /* __KERNEL__ */ static __inline__ __be32 inet_make_mask(int logmask) diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c index c4b396968acd6..ed9ef8430c14f 100644 --- a/net/ipv4/igmp.c +++ b/net/ipv4/igmp.c @@ -237,16 +237,20 @@ static void igmp_gq_start_timer(struct in_device *in_dev) return; in_dev->mr_gq_running = 1; - if (!mod_timer(&in_dev->mr_gq_timer, exp)) - in_dev_hold(in_dev); + if (in_dev_hold_safe(in_dev)) { + if (mod_timer(&in_dev->mr_gq_timer, exp)) + in_dev_put(in_dev); + } } static void igmp_ifc_start_timer(struct in_device *in_dev, int delay) { - int tv = prandom_u32() % delay; + if (in_dev_hold_safe(in_dev)) { + int tv = prandom_u32() % (delay); - if (!mod_timer(&in_dev->mr_ifc_timer, jiffies+tv+2)) - in_dev_hold(in_dev); + if (mod_timer(&in_dev->mr_ifc_timer, jiffies + tv + 2)) + in_dev_put(in_dev); + } } static void igmp_mod_timer(struct ip_mc_list *im, int max_delay) -- 2.33.8