[PATCH 3.16 134/366] fs/proc/proc_sysctl.c: fix potential page fault while unregistering sysctl table

From: Ben Hutchings
Date: Sun Oct 14 2018 - 11:33:49 EST


3.16.60-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Danilo Krummrich <danilokrummrich@xxxxxxxxxxxxx>

commit a0b0d1c345d0317efe594df268feb5ccc99f651e upstream.

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: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
fs/proc/proc_sysctl.c | 3 +++
1 file changed, 3 insertions(+)

--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -654,7 +654,10 @@ 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 */