4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx> [ Upstream commit a0b0d1c345d0317efe594df268feb5ccc99f651e ] 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. Link: http://lkml.kernel.org/r/20180228013506.4915-1-danilokrummrich@xxxxxxxxxxxxx Fixes: 0e47c99d7fe25 ("sysctl: Replace root_list with links between sysctl_table_sets") Signed-off-by: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: "Luis R . Rodriguez" <mcgrof@xxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/proc/proc_sysctl.c | 3 +++ 1 file changed, 3 insertions(+) --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -707,7 +707,10 @@ static bool proc_sys_link_fill_cache(str 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 */
