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Wysocki" , Yury Norov , Phil Auld , Sasha Levin Subject: [PATCH 5.15 018/136] drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist Date: Mon, 29 Aug 2022 12:58:05 +0200 Message-Id: <20220829105805.358034570@linuxfoundation.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220829105804.609007228@linuxfoundation.org> References: <20220829105804.609007228@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Phil Auld [ Upstream commit 7ee951acd31a88f941fd6535fbdee3a1567f1d63 ] Using bin_attributes with a 0 size causes fstat and friends to return that 0 size. This breaks userspace code that retrieves the size before reading the file. Rather than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI") let's put in a size value at compile time. For cpulist the maximum size is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1)/2 which for 8192 is 20480 (8192 * 5)/2. In order to get near that you'd need a system with every other CPU on one node. For example: (0,2,4,8, ... ). To simplify the math and support larger NR_CPUS in the future we are using (NR_CPUS * 7)/2. We also set it to a min of PAGE_SIZE to retain the older behavior for smaller NR_CPUS. The cpumap file the size works out to be NR_CPUS/4 + NR_CPUS/32 - 1 (or NR_CPUS * 9/32 - 1) including the ","s. Add a set of macros for these values to cpumask.h so they can be used in multiple places. Apply these to the handful of such files in drivers/base/topology.c as well as node.c. As an example, on an 80 cpu 4-node system (NR_CPUS == 8192): before: -r--r--r--. 1 root root 0 Jul 12 14:08 system/node/node0/cpulist -r--r--r--. 1 root root 0 Jul 11 17:25 system/node/node0/cpumap after: -r--r--r--. 1 root root 28672 Jul 13 11:32 system/node/node0/cpulist -r--r--r--. 1 root root 4096 Jul 13 11:31 system/node/node0/cpumap CONFIG_NR_CPUS = 16384 -r--r--r--. 1 root root 57344 Jul 13 14:03 system/node/node0/cpulist -r--r--r--. 1 root root 4607 Jul 13 14:02 system/node/node0/cpumap The actual number of cpus doesn't matter for the reported size since they are based on NR_CPUS. Fixes: 75bd50fa841d ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI") Fixes: bb9ec13d156e ("topology: use bin_attribute to break the size limitation of cpumap ABI") Cc: Greg Kroah-Hartman Cc: "Rafael J. Wysocki" Cc: Yury Norov Cc: stable@vger.kernel.org Acked-by: Yury Norov (for include/linux/cpumask.h) Signed-off-by: Phil Auld Link: https://lore.kernel.org/r/20220715134924.3466194-1-pauld@redhat.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/base/node.c | 4 ++-- drivers/base/topology.c | 28 ++++++++++++++-------------- include/linux/cpumask.h | 18 ++++++++++++++++++ 3 files changed, 34 insertions(+), 16 deletions(-) diff --git a/drivers/base/node.c b/drivers/base/node.c index 0f5319b79fadc..5366d1b5359c8 100644 --- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj, return n; } -static BIN_ATTR_RO(cpumap, 0); +static BIN_ATTR_RO(cpumap, CPUMAP_FILE_MAX_BYTES); static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj, struct bin_attribute *attr, char *buf, @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj, return n; } -static BIN_ATTR_RO(cpulist, 0); +static BIN_ATTR_RO(cpulist, CPULIST_FILE_MAX_BYTES); /** * struct node_access_nodes - Access class device to hold user visible diff --git a/drivers/base/topology.c b/drivers/base/topology.c index 43c0940643f5d..5df6d861bc21b 100644 --- a/drivers/base/topology.c +++ b/drivers/base/topology.c @@ -52,39 +52,39 @@ define_id_show_func(core_id); static DEVICE_ATTR_RO(core_id); define_siblings_read_func(thread_siblings, sibling_cpumask); -static BIN_ATTR_RO(thread_siblings, 0); -static BIN_ATTR_RO(thread_siblings_list, 0); +static BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES); define_siblings_read_func(core_cpus, sibling_cpumask); -static BIN_ATTR_RO(core_cpus, 0); -static BIN_ATTR_RO(core_cpus_list, 0); +static BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES); define_siblings_read_func(core_siblings, core_cpumask); -static BIN_ATTR_RO(core_siblings, 0); -static BIN_ATTR_RO(core_siblings_list, 0); +static BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES); define_siblings_read_func(die_cpus, die_cpumask); -static BIN_ATTR_RO(die_cpus, 0); -static BIN_ATTR_RO(die_cpus_list, 0); +static BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES); define_siblings_read_func(package_cpus, core_cpumask); -static BIN_ATTR_RO(package_cpus, 0); -static BIN_ATTR_RO(package_cpus_list, 0); +static BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES); #ifdef CONFIG_SCHED_BOOK define_id_show_func(book_id); static DEVICE_ATTR_RO(book_id); define_siblings_read_func(book_siblings, book_cpumask); -static BIN_ATTR_RO(book_siblings, 0); -static BIN_ATTR_RO(book_siblings_list, 0); +static BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES); #endif #ifdef CONFIG_SCHED_DRAWER define_id_show_func(drawer_id); static DEVICE_ATTR_RO(drawer_id); define_siblings_read_func(drawer_siblings, drawer_cpumask); -static BIN_ATTR_RO(drawer_siblings, 0); -static BIN_ATTR_RO(drawer_siblings_list, 0); +static BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES); +static BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES); #endif static struct bin_attribute *bin_attrs[] = { diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index 1e7399fc69c0a..054e654f06def 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -1045,4 +1045,22 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, [0] = 1UL \ } } +/* + * Provide a valid theoretical max size for cpumap and cpulist sysfs files + * to avoid breaking userspace which may allocate a buffer based on the size + * reported by e.g. fstat. + * + * for cpumap NR_CPUS * 9/32 - 1 should be an exact length. + * + * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up + * to 2 orders of magnitude larger than 8192. And then we divide by 2 to + * cover a worst-case of every other cpu being on one of two nodes for a + * very large NR_CPUS. + * + * Use PAGE_SIZE as a minimum for smaller configurations. + */ +#define CPUMAP_FILE_MAX_BYTES ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \ + ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE) +#define CPULIST_FILE_MAX_BYTES (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE) + #endif /* __LINUX_CPUMASK_H */ -- 2.35.1