From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A5ADE455639; Sat, 12 Sep 2026 10:45:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789209960; cv=none; b=kFovC5022+ql+4BN2cDCe7MEuqcZMGZ8qxBy/M+HmtC9GXGi8RIkiERa39l20YxlDVRbd4Wj7jtXYK/kYXySAtcXalG7GHHsqCqD7x/6WKg5INdrPn9ro2l/9MyHkqazOeWp4DG1fliCoPEfsxnWMR4SXt/i0J/qy1nVdh+A7UQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789209960; c=relaxed/simple; bh=3HcyFSzHm7EpP+Sg4jCCHTipsVE461JJnlkuNjOSkA0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=IGmBvHo7LUtsVNR53lWmbClObCxmDTsLwL7bdZnccB0TEClrL+8T71k9n7IEfGUX8uDtU5QKPmvGGKFghwFikfPybp+in87kDVj3RVM9R9NF3MKY/Xg67o2UnPm/KzapLPETrAR9DnQyyg8tVQRsUtvmG/d7aCwiZso/DvBUZRc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=CJwINGS3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="CJwINGS3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7EBFE1F000FF; Sat, 12 Sep 2026 10:45:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789209958; bh=y6L0NwFFX2KjfYMz0KcbQQmL0acL1kCeMS3pnhd1hg4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=CJwINGS3jzfXC+6CA/MwV8o9GhRFOHNjIZuN+NaAY43R4Ghcp4yaZ0bjhPsKml2eX s3NYbYHFxwSqSKOLHfvGY1XIrpwvASXjUDuwVzODIn/aEz590CPuETbDVW/2PfXXZF Zbw/Pc2FgbxJPUz1e1TGH07lGWxvN1XZEJieskmc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Aaron Tomlin , Petr Pavlu , Sasha Levin Subject: [PATCH 6.18 0929/1518] module/dups: Fix use-after-free in kmod_dup_req lifetime handling Date: Sat, 12 Sep 2026 08:51:38 +0200 Message-ID: <20260912065644.467017497@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065623.398859879@linuxfoundation.org> References: <20260912065623.398859879@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Petr Pavlu [ Upstream commit 5eecb11b543f9f417bcf0dea239ff99c6af65dbd ] The kmod dups code uses RCU to ensure that a kmod_dup_req instance is freed only after it is no longer referenced. When releasing an instance, the kmod_dup_request_delete() function removes the kmod_dup_req from the dup_kmod_reqs list, waits via synchronize_rcu() and finally frees it. However, this doesn't work correctly because parallel users referencing the instance in kmod_dup_request_exists_wait() don't enter an RCU read-side critical section. This can result in a use-after-free. The kmod_dup_request_exists_wait() function may need to hold a valid reference to a kmod_dup_req instance across a blocking wait until the corresponding modprobe command completes. This makes it unsuitable for RCU. Fix the issue by changing the lifecycle management of kmod_dup_req to use reference counting. Fixes: 8660484ed1cf ("module: add debugging auto-load duplicate module support") Reviewed-by: Aaron Tomlin Signed-off-by: Petr Pavlu Signed-off-by: Sasha Levin --- kernel/module/dups.c | 56 +++++++++++++++++++++++++++++++------------- 1 file changed, 40 insertions(+), 16 deletions(-) diff --git a/kernel/module/dups.c b/kernel/module/dups.c index 7b9b08031d7d2..c21b675c239b7 100644 --- a/kernel/module/dups.c +++ b/kernel/module/dups.c @@ -30,6 +30,7 @@ #include #include #include +#include #include "internal.h" @@ -38,13 +39,12 @@ static bool enable_dups_trace = IS_ENABLED(CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS_TRACE); module_param(enable_dups_trace, bool_enable_only, 0644); -/* - * Protects dup_kmod_reqs list, adds / removals with RCU. - */ +/* A mutex-protected list of active kmod requests. */ static DEFINE_MUTEX(kmod_dup_mutex); static LIST_HEAD(dup_kmod_reqs); struct kmod_dup_req { + refcount_t refcount; struct list_head list; char name[MODULE_NAME_LEN]; struct completion first_req_done; @@ -52,12 +52,24 @@ struct kmod_dup_req { int dup_ret; }; +static void get_kmod_req(struct kmod_dup_req *kmod_req) +{ + refcount_inc(&kmod_req->refcount); +} + +static void put_kmod_req(struct kmod_dup_req *kmod_req) +{ + if (refcount_dec_and_test(&kmod_req->refcount)) + kfree(kmod_req); +} + static struct kmod_dup_req *kmod_dup_request_lookup(char *module_name) { struct kmod_dup_req *kmod_req; - list_for_each_entry_rcu(kmod_req, &dup_kmod_reqs, list, - lockdep_is_held(&kmod_dup_mutex)) { + lockdep_assert_held(&kmod_dup_mutex); + + list_for_each_entry(kmod_req, &dup_kmod_reqs, list) { if (strlen(kmod_req->name) == strlen(module_name) && !memcmp(kmod_req->name, module_name, strlen(module_name))) { return kmod_req; @@ -86,10 +98,10 @@ static void kmod_dup_request_delete(struct work_struct *work) * just returning 0. */ mutex_lock(&kmod_dup_mutex); - list_del_rcu(&kmod_req->list); - synchronize_rcu(); + list_del(&kmod_req->list); mutex_unlock(&kmod_dup_mutex); - kfree(kmod_req); + + put_kmod_req(kmod_req); } bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret) @@ -105,6 +117,7 @@ bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret) if (!new_kmod_req) return false; + refcount_set(&new_kmod_req->refcount, 1); strscpy(new_kmod_req->name, module_name); INIT_DELAYED_WORK(&new_kmod_req->delete_work, kmod_dup_request_delete); init_completion(&new_kmod_req->first_req_done); @@ -136,10 +149,12 @@ bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret) * keep tab on duplicates later. */ pr_debug("New request_module() for %s\n", module_name); - list_add_rcu(&new_kmod_req->list, &dup_kmod_reqs); + list_add(&new_kmod_req->list, &dup_kmod_reqs); mutex_unlock(&kmod_dup_mutex); return false; } + + get_kmod_req(kmod_req); mutex_unlock(&kmod_dup_mutex); /* We are dealing with a duplicate request now */ @@ -169,7 +184,7 @@ bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret) * calls bail out right away. */ *dup_ret = 0; - return true; + goto out; } /* @@ -184,12 +199,14 @@ bool kmod_dup_request_exists_wait(char *module_name, bool wait, int *dup_ret) TASK_KILLABLE); if (ret) { *dup_ret = ret; - return true; + goto out; } /* Now the duplicate request has the same exact return value as the first request */ *dup_ret = kmod_req->dup_ret; +out: + put_kmod_req(kmod_req); return true; } @@ -199,15 +216,25 @@ void kmod_dup_request_announce(char *module_name, int ret) mutex_lock(&kmod_dup_mutex); + /* + * Look for a kmod_dup_req previously added in + * kmod_dup_request_exists_wait(). Note that a request_module_nowait() + * without its own kmod_dup_req entry can announce a result of + * a concurrent request_module() call. + */ kmod_req = kmod_dup_request_lookup(module_name); - if (!kmod_req) - goto out; + if (!kmod_req || completion_done(&kmod_req->first_req_done)) { + mutex_unlock(&kmod_dup_mutex); + return; + } kmod_req->dup_ret = ret; /* Inform all duplicate waiters to check the return value. */ complete_all(&kmod_req->first_req_done); + mutex_unlock(&kmod_dup_mutex); + /* * Now that we have allowed prior request_module() calls to go on * with life, let's schedule deleting this entry. We don't have @@ -216,7 +243,4 @@ void kmod_dup_request_announce(char *module_name, int ret) * possible abuses of vmalloc() incurred by finit_module() thrashing. */ queue_delayed_work(system_dfl_wq, &kmod_req->delete_work, 60 * HZ); - -out: - mutex_unlock(&kmod_dup_mutex); } -- 2.53.0