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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id n7-20020a170902d2c700b001cc52ca2dfbsm1800902plc.120.2023.11.30.12.12.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Nov 2023 12:12:25 -0800 (PST) From: Kees Cook To: Greg Kroah-Hartman Cc: Kees Cook , Tejun Heo , Zefan Li , Johannes Weiner , Waiman Long , cgroups@vger.kernel.org, Azeem Shaikh , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 3/3] kernfs: Convert kernfs_path_from_node_locked() from strlcpy() to strscpy() Date: Thu, 30 Nov 2023 12:12:19 -0800 Message-Id: <20231130201222.3613535-3-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20231130200937.it.424-kees@kernel.org> References: <20231130200937.it.424-kees@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=8106; i=keescook@chromium.org; h=from:subject; bh=ytYczlvWwngfOAhKBEd29zggKM1dZYUFgsNew6TNfcc=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlaOyjjwlnfJ6o+rRxKIqAd0jCo71AoDJUjPpjY YoJBoDBvPWJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZWjsowAKCRCJcvTf3G3A JkPUD/90GudFsO1LYNdR1bciTGcerJiWBv2OIofG6858EQVJUxJIy77PoKrYXozBwoPcfnsC+GD zy7am0RcN4EDnQdqH8l+VezpYkFjVdhE3VTSEGyD37n5L90dTTf4Ko7u6pC+fWt0db5mTotni+L ozR/VRxweZuhlkxvb3pvfmBUF3qrnomBRIs6T3FFK3iy87pwtW7dDKpHs+AZNfopDZIrdxaXmGL H9yEGTdMxCk7RqGWS8ZPJBtMLtUuEGDmwpCiC9KcxIhMnKPx8J05OLUXizl38IrKn1me65Rqivv UUpZolnF6jUmpNvKLG/kn0KCZAqtZm74QZFet4VH/k+qsHfZv+gG5oBVDHUcuwhWrSbiTYEjRoH GoSqPQE4lwwx3p1I0xUa9samPc/0lnKVbi5O6TIIxjAa4HmO/KTDFOnZCHmbGJUfbjvMzKVEK9Y tJpiiqkWffLMWl4QrwD8+ws8E5HP3l3hRX6o58VH64Nb3hV8jlvZlt8tCKreY+gRsRNedQVvNgZ aOL8Tr7PqUhRqe95IHxKpun7DKTZrM6+0hWER/rHNQqtfIJueAMQMOrPyHwklNqZajUEjLr1UHe 32zNNc/W45HOmSB32VYD2gHGvlwnS1+jONUOIj9zOxZVr0hT9NMwZbKeW65j/9nD+WsAZdPHoFx MLC/0IKHoha7fNA== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 One of the last remaining users of strlcpy() in the kernel is kernfs_path_from_node_locked(), which passes back the problematic "length we _would_ have copied" return value to indicate truncation. Convert the chain of all callers to use the negative return value (some of which already doing this explicitly). All callers were already also checking for negative return values, so the risk to missed checks looks very low. In this analysis, it was found that cgroup1_release_agent() actually didn't handle the "too large" condition, so this is technically also a bug fix. :) Here's the chain of callers, and resolution identifying each one as now handling the correct return value: kernfs_path_from_node_locked() kernfs_path_from_node() pr_cont_kernfs_path() returns void kernfs_path() sysfs_warn_dup() return value ignored cgroup_path() blkg_path() bfq_bic_update_cgroup() return value ignored TRACE_IOCG_PATH() return value ignored TRACE_CGROUP_PATH() return value ignored perf_event_cgroup() return value ignored task_group_path() return value ignored damon_sysfs_memcg_path_eq() return value ignored get_mm_memcg_path() return value ignored lru_gen_seq_show() return value ignored cgroup_path_from_kernfs_id() return value ignored cgroup_show_path() already converted "too large" error to negative value cgroup_path_ns_locked() cgroup_path_ns() bpf_iter_cgroup_show_fdinfo() return value ignored cgroup1_release_agent() wasn't checking "too large" error proc_cgroup_show() already converted "too large" to negative value Cc: Greg Kroah-Hartman Cc: Tejun Heo Cc: Zefan Li Cc: Johannes Weiner Cc: Waiman Long Cc: cgroups@vger.kernel.org Co-developed-by: Azeem Shaikh Signed-off-by: Azeem Shaikh Link: https://lore.kernel.org/r/20231116192127.1558276-3-keescook@chromium.org Signed-off-by: Kees Cook --- fs/kernfs/dir.c | 37 ++++++++++++++++++++----------------- kernel/cgroup/cgroup-v1.c | 2 +- kernel/cgroup/cgroup.c | 4 ++-- kernel/cgroup/cpuset.c | 2 +- 4 files changed, 24 insertions(+), 21 deletions(-) diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c index 8c0e5442597e..183f353b3852 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -127,7 +127,7 @@ static struct kernfs_node *kernfs_common_ancestor(struct kernfs_node *a, * * [3] when @kn_to is %NULL result will be "(null)" * - * Return: the length of the full path. If the full length is equal to or + * Return: the length of the constructed path. If the path would have been * greater than @buflen, @buf contains the truncated path with the trailing * '\0'. On error, -errno is returned. */ @@ -138,16 +138,17 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, struct kernfs_node *kn, *common; const char parent_str[] = "/.."; size_t depth_from, depth_to, len = 0; + ssize_t copied; int i, j; if (!kn_to) - return strlcpy(buf, "(null)", buflen); + return strscpy(buf, "(null)", buflen); if (!kn_from) kn_from = kernfs_root(kn_to)->kn; if (kn_from == kn_to) - return strlcpy(buf, "/", buflen); + return strscpy(buf, "/", buflen); common = kernfs_common_ancestor(kn_from, kn_to); if (WARN_ON(!common)) @@ -158,18 +159,22 @@ static int kernfs_path_from_node_locked(struct kernfs_node *kn_to, buf[0] = '\0'; - for (i = 0; i < depth_from; i++) - len += strlcpy(buf + len, parent_str, - len < buflen ? buflen - len : 0); + for (i = 0; i < depth_from; i++) { + copied = strscpy(buf + len, parent_str, buflen - len); + if (copied < 0) + return copied; + len += copied; + } /* Calculate how many bytes we need for the rest */ for (i = depth_to - 1; i >= 0; i--) { for (kn = kn_to, j = 0; j < i; j++) kn = kn->parent; - len += strlcpy(buf + len, "/", - len < buflen ? buflen - len : 0); - len += strlcpy(buf + len, kn->name, - len < buflen ? buflen - len : 0); + + copied = scnprintf(buf + len, buflen - len, "/%s", kn->name); + if (copied < 0) + return copied; + len += copied; } return len; @@ -214,7 +219,7 @@ int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen) * path (which includes '..'s) as needed to reach from @from to @to is * returned. * - * Return: the length of the full path. If the full length is equal to or + * Return: the length of the constructed path. If the path would have been * greater than @buflen, @buf contains the truncated path with the trailing * '\0'. On error, -errno is returned. */ @@ -265,12 +270,10 @@ void pr_cont_kernfs_path(struct kernfs_node *kn) sz = kernfs_path_from_node(kn, NULL, kernfs_pr_cont_buf, sizeof(kernfs_pr_cont_buf)); if (sz < 0) { - pr_cont("(error)"); - goto out; - } - - if (sz >= sizeof(kernfs_pr_cont_buf)) { - pr_cont("(name too long)"); + if (sz == -E2BIG) + pr_cont("(name too long)"); + else + pr_cont("(error)"); goto out; } diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c index 76db6c67e39a..9cb00ebe9ac6 100644 --- a/kernel/cgroup/cgroup-v1.c +++ b/kernel/cgroup/cgroup-v1.c @@ -802,7 +802,7 @@ void cgroup1_release_agent(struct work_struct *work) goto out_free; ret = cgroup_path_ns(cgrp, pathbuf, PATH_MAX, &init_cgroup_ns); - if (ret < 0 || ret >= PATH_MAX) + if (ret < 0) goto out_free; argv[0] = agentbuf; diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 4b9ff41ca603..8d2674c6aaef 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1893,7 +1893,7 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node, len = kernfs_path_from_node(kf_node, ns_cgroup->kn, buf, PATH_MAX); spin_unlock_irq(&css_set_lock); - if (len >= PATH_MAX) + if (len == -E2BIG) len = -ERANGE; else if (len > 0) { seq_escape(sf, buf, " \t\n\\"); @@ -6301,7 +6301,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns, if (cgroup_on_dfl(cgrp) || !(tsk->flags & PF_EXITING)) { retval = cgroup_path_ns_locked(cgrp, buf, PATH_MAX, current->nsproxy->cgroup_ns); - if (retval >= PATH_MAX) + if (retval == -E2BIG) retval = -ENAMETOOLONG; if (retval < 0) goto out_unlock; diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 615daaf87f1f..fb29158ae825 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -4941,7 +4941,7 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns, retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX, current->nsproxy->cgroup_ns); css_put(css); - if (retval >= PATH_MAX) + if (retval == -E2BIG) retval = -ENAMETOOLONG; if (retval < 0) goto out_free;