linux-kernel - [PATCH v3 1/2] fs/sysctl: fix potential page fault while unregistering sysctl table

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Message-Id: <20180228013506.4915-1-danilokrummrich@dk-develop.de>
Date:   Wed, 28 Feb 2018 02:35:05 +0100
From:   Danilo Krummrich <danilokrummrich@...develop.de>
To:     mcgrof@...nel.org, keescook@...omium.org, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Danilo Krummrich <danilokrummrich@...develop.de>,
        stable@...r.kernel.org
Subject: [PATCH v3 1/2] fs/sysctl: fix potential page fault while unregistering sysctl table

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@...r.kernel.org
Acked-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Danilo Krummrich <danilokrummrich@...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 */
-- 
2.14.1