Patch "drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist" has been added to the 5.15-stable tree

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This is a note to let you know that I've just added the patch titled

    drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drivers-base-fix-userspace-break-from-using-bin_attr.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 40c1b27ca3a22ee15423a5f6e890084576809c2b
Author: Phil Auld <pauld@xxxxxxxxxx>
Date:   Fri Jul 15 09:49:24 2022 -0400

    drivers/base: fix userspace break from using bin_attributes for cpumap and cpulist
    
    [ 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 <gregkh@xxxxxxxxxxxxxxxxxxx>
    Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
    Cc: Yury Norov <yury.norov@xxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Acked-by: Yury Norov <yury.norov@xxxxxxxxx> (for include/linux/cpumask.h)
    Signed-off-by: Phil Auld <pauld@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220715134924.3466194-1-pauld@xxxxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 0f5319b79fad..5366d1b5359c 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 9d049724e4b4..4c8328468e97 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -59,47 +59,47 @@ 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);
 
 #ifdef TOPOLOGY_CLUSTER_SYSFS
 define_siblings_read_func(cluster_cpus, cluster_cpumask);
-static BIN_ATTR_RO(cluster_cpus, 0);
-static BIN_ATTR_RO(cluster_cpus_list, 0);
+static BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES);
+static BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES);
 #endif
 
 #ifdef TOPOLOGY_DIE_SYSFS
 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);
 #endif
 
 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 1e7399fc69c0..054e654f06de 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 */



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