diff options
| author | Kees Cook <keescook@chromium.org> | 2014-12-12 13:36:49 +1030 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2014-12-18 12:38:51 +1030 |
| commit | b0a65b0cccd477b2fd8b7adad0ac39433df54829 (patch) | |
| tree | cd34e0b1dfae25117f114becd0b5153133193098 | |
| parent | 18eb74fa94161380c1acc9cf562cb835c4e54a25 (diff) | |
| download | linux-b0a65b0cccd477b2fd8b7adad0ac39433df54829.tar.bz2 | |
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>
| -rw-r--r-- | kernel/params.c | 4 |
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++; |