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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")
Acked-by: Kees Cook <>
Signed-off-by: Danilo Krummrich <>
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 */
 \ /
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