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

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

[Danilo Krummrich]

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 */
-- 
2.14.1

[PATCH v3 2/2] fs/sysctl: remove redundant link check in proc_sys_link_fill_cache()

[Danilo Krummrich]

proc_sys_link_fill_cache() does not need to check whether we're
called for a link - it's already done by scan().

Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Danilo Krummrich <danilokrummrich@dk-develop.de>
---
v2: removed 'err' as it's only used for sysctl_follow_link()
v3: add ack
---
 fs/proc/proc_sysctl.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 82ac5f682b73..d36ef667c0a8 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -712,12 +712,9 @@ static bool proc_sys_link_fill_cache(struct file *file,
 	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 */
-		int err = sysctl_follow_link(&head, &table);
-		if (err)
-			goto out;
-	}
+	/* It is not an error if we can not follow the link ignore it */
+	if (sysctl_follow_link(&head, &table))
+		goto out;
 
 	ret = proc_sys_fill_cache(file, ctx, head, table);
 out:
-- 
2.14.1