summaryrefslogtreecommitdiff
path: root/kernel/params.c
diff options
context:
space:
mode:
authorKees Cook <keescook@chromium.org>2014-12-12 13:36:49 +1030
committerRusty Russell <rusty@rustcorp.com.au>2014-12-18 12:38:51 +1030
commitb0a65b0cccd477b2fd8b7adad0ac39433df54829 (patch)
treecd34e0b1dfae25117f114becd0b5153133193098 /kernel/params.c
parent18eb74fa94161380c1acc9cf562cb835c4e54a25 (diff)
downloadlinux-sh-b0a65b0cccd477b2fd8b7adad0ac39433df54829.tar.gz
param: do not set store func without write perm
When a module_param is defined without DAC write permissions, it can still be changed at runtime and updated. Drivers using a 0444 permission may be surprised that these values can still be changed. For drivers that want to allow updates, any S_IW* flag will set the "store" function as before. Drivers without S_IW* flags will have the "store" function unset, unforcing a read-only value. Drivers that wish neither "store" nor "get" can continue to use "0" for perms to stay out of sysfs entirely. Old behavior: # cd /sys/module/snd/parameters # ls -l total 0 -r--r--r-- 1 root root 4096 Dec 11 13:55 cards_limit -r--r--r-- 1 root root 4096 Dec 11 13:55 major -r--r--r-- 1 root root 4096 Dec 11 13:55 slots # cat major 116 # echo -1 > major -bash: major: Permission denied # chmod u+w major # echo -1 > major # cat major -1 New behavior: ... # chmod u+w major # echo -1 > major -bash: echo: write error: Input/output error Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'kernel/params.c')
-rw-r--r--kernel/params.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/kernel/params.c b/kernel/params.c
index 795321aba29f..0af9b2c4e56c 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -645,7 +645,9 @@ static __modinit int add_sysfs_param(struct module_kobject *mk,
sysfs_attr_init(&mk->mp->attrs[mk->mp->num].mattr.attr);
mk->mp->attrs[mk->mp->num].param = kp;
mk->mp->attrs[mk->mp->num].mattr.show = param_attr_show;
- mk->mp->attrs[mk->mp->num].mattr.store = param_attr_store;
+ /* Do not allow runtime DAC changes to make param writable. */
+ if ((kp->perm & (S_IWUSR | S_IWGRP | S_IWOTH)) != 0)
+ mk->mp->attrs[mk->mp->num].mattr.store = param_attr_store;
mk->mp->attrs[mk->mp->num].mattr.attr.name = (char *)name;
mk->mp->attrs[mk->mp->num].mattr.attr.mode = kp->perm;
mk->mp->num++;