On 13.11.2019 6.50, Andy Lutomirski wrote:
On Tue, Nov 12, 2019 at 3:22 PM Christian Brauner
<christian.brauner@xxxxxxxxxx> wrote:
[Cc+ linux-api@xxxxxxxxxxxxxxx]
since that's potentially relevant to quite a few people.
On Sun, Nov 03, 2019 at 04:55:48PM +0200, Topi Miettinen wrote:
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@xxxxxxxxx>
---
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;
Supporting at least ATTR_GID would make this much more useful.
Yes, also XATTR/ACL support would be useful. But so far I've tried to
allow only tightening of permissions.
+ 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;
Style nit: please put braces around multi-line if and else branches,
even if they're only multi-line because of comments.
OK, thanks.
+
+ sysctl_head_finish(head);
+
+ /* Execute bits only allowed for directories */
+ if (!S_ISDIR(inode->i_mode))
+ max_mode &= ~0111;
Why is this needed?
In general, /proc/sys does not allow executable permissions for the
files, so I've continued this policy.
-Topi
