proc_sys_link_fill_cache() does not take currently unregistering sysctl tables into account, which might result into a page fault in sysctl_follow_link() - add a check to fix it.

This bug has been present since v3.4.

Fixes: 0e47c99d7fe25 ("sysctl: Replace root_list with links between sysctl_table_sets") Cc: stable@vger.kernel.org Acked-by: Kees Cook keescook@chromium.org Signed-off-by: Danilo Krummrich danilokrummrich@dk-develop.de --- v2: removed empty line between between sysctl_head_grab and IS_ERR v3: extend commit message, add tags and cc stable --- fs/proc/proc_sysctl.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c index c5cbbdff3c3d..82ac5f682b73 100644 --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -707,7 +707,10 @@ static bool proc_sys_link_fill_cache(struct file *file, struct ctl_table *table) { bool ret = true; + head = sysctl_head_grab(head); + if (IS_ERR(head)) + return false;

if (S_ISLNK(table->mode)) { /* It is not an error if we can not follow the link ignore it */