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Message-ID: <74a91362-247c-c749-5200-7bdce704ed9e@gmail.com>
Date: Sun, 3 Nov 2019 16:55:48 +0200
From: Topi Miettinen <toiwoton@...il.com>
To: Luis Chamberlain <mcgrof@...nel.org>,
Kees Cook <keescook@...omium.org>,
Alexey Dobriyan <adobriyan@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"open list:FILESYSTEMS (VFS and infrastructure)"
<linux-fsdevel@...r.kernel.org>
Subject: [PATCH] Allow restricting permissions in /proc/sys
Several items in /proc/sys need not be accessible to unprivileged
tasks. Let the system administrator change the permissions, but only
to more restrictive modes than what the sysctl tables allow.
Signed-off-by: Topi Miettinen <toiwoton@...il.com>
---
fs/proc/proc_sysctl.c | 41 +++++++++++++++++++++++++++++++----------
1 file changed, 31 insertions(+), 10 deletions(-)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index d80989b6c344..88c4ca7d2782 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -818,6 +818,10 @@ static int proc_sys_permission(struct inode *inode,
int mask)
if ((mask & MAY_EXEC) && S_ISREG(inode->i_mode))
return -EACCES;
+ error = generic_permission(inode, mask);
+ if (error)
+ return error;
+
head = grab_header(inode);
if (IS_ERR(head))
return PTR_ERR(head);
@@ -837,9 +841,35 @@ static int proc_sys_setattr(struct dentry *dentry,
struct iattr *attr)
struct inode *inode = d_inode(dentry);
int error;
- if (attr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
+ if (attr->ia_valid & (ATTR_UID | ATTR_GID))
return -EPERM;
+ if (attr->ia_valid & ATTR_MODE) {
+ struct ctl_table_header *head = grab_header(inode);
+ struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+ umode_t max_mode = 0777; /* Only these bits may change */
+
+ if (IS_ERR(head))
+ return PTR_ERR(head);
+
+ if (!table) /* global root - r-xr-xr-x */
+ max_mode &= ~0222;
+ else /*
+ * Don't allow permissions to become less
+ * restrictive than the sysctl table entry
+ */
+ max_mode &= table->mode;
+
+ sysctl_head_finish(head);
+
+ /* Execute bits only allowed for directories */
+ if (!S_ISDIR(inode->i_mode))
+ max_mode &= ~0111;
+
+ if (attr->ia_mode & ~S_IFMT & ~max_mode)
+ return -EPERM;
+ }
+
error = setattr_prepare(dentry, attr);
if (error)
return error;
@@ -853,17 +883,8 @@ static int proc_sys_getattr(const struct path
*path, struct kstat *stat,
u32 request_mask, unsigned int query_flags)
{
struct inode *inode = d_inode(path->dentry);
- struct ctl_table_header *head = grab_header(inode);
- struct ctl_table *table = PROC_I(inode)->sysctl_entry;
-
- if (IS_ERR(head))
- return PTR_ERR(head);
generic_fillattr(inode, stat);
- if (table)
- stat->mode = (stat->mode & S_IFMT) | table->mode;
-
- sysctl_head_finish(head);
return 0;
}
--
2.24.0.rc1
View attachment "0001-Allow-restricting-permissions-in-proc-sys.patch" of type "text/x-diff" (2599 bytes)
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