[Devel] [PATCH] fs: Fix invalid dereference in proc_sys_getattr()

[Kirill Tkhai]

grab_header() may return -ENOENT. In this case root in the below

        struct ctl_table_header *head = grab_header(inode);
	struct ctl_table_root *root = head->root;

dereferences (void *)-ENOENT, that leads to page fault and crash.
Fix that.

https://jira.sw.ru/browse/PSBM-56704

Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 fs/proc/proc_sysctl.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 1727eabfb4e..3c05a5592e3 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -758,12 +758,14 @@ static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct
 {
 	struct inode *inode = dentry->d_inode;
 	struct ctl_table_header *head = grab_header(inode);
-	struct ctl_table_root *root = head->root;
 	struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+	struct ctl_table_root *root;
 
 	if (IS_ERR(head))
 		return PTR_ERR(head);
 
+	root = head->root;
+
 	generic_fillattr(inode, stat);
 
 	if (table) {