[PATCH] avoid multiplication overflows and signedness issues for max_fds

Limit sysctl_nr_open - we don't want ->max_fds to exceed MAX_INT and
we don't want size calculation for ->fd[] to overflow.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 8 insertions, 1 deletions

diff --git a/fs/file.c b/fs/file.c
index 0f705c7cfefe..7b3887e054d0 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -26,6 +26,8 @@ struct fdtable_defer {
 };
 
 int sysctl_nr_open __read_mostly = 1024*1024;
+int sysctl_nr_open_min = BITS_PER_LONG;
+int sysctl_nr_open_max = 1024 * 1024; /* raised later */
 
 /*
  * We use this list to defer free fdtables that have vmalloced
@@ -405,6 +407,8 @@ void __init files_defer_init(void)
         int i;
         for_each_possible_cpu(i)
                 fdtable_defer_list_init(i);
+        sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
+                             -BITS_PER_LONG;
 }
 
 struct files_struct init_files = {
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index d7ffdc59816a..29116652dca8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -81,6 +81,7 @@ extern int compat_log;
 extern int maps_protect;
 extern int sysctl_stat_interval;
 extern int latencytop_enabled;
+extern int sysctl_nr_open_min, sysctl_nr_open_max;
 
 /* Constants used for minimum and  maximum */
 #if defined(CONFIG_DETECT_SOFTLOCKUP) || defined(CONFIG_HIGHMEM)
@@ -1190,7 +1191,9 @@ static struct ctl_table fs_table[] = {
                 .data           = &sysctl_nr_open,
                 .maxlen         = sizeof(int),
                 .mode           = 0644,
-                .proc_handler   = &proc_dointvec,
+                .proc_handler   = &proc_dointvec_minmax,
+                .extra1         = &sysctl_nr_open_min,
+                .extra2         = &sysctl_nr_open_max,
         },
         {
                 .ctl_name       = FS_DENTRY,