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security: Add LSM hooks to set*gid syscalls

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The SafeSetID LSM uses the security_task_fix_setuid hook to filter
set*uid() syscalls according to its configured security policy. In
preparation for adding analagous support in the LSM for set*gid()
syscalls, we add the requisite hook here. Tested by putting print
statements in the security_task_fix_setgid hook and seeing them get hit
during kernel boot.

Signed-off-by: Thomas Cedeno <thomascedeno@google.com>
Signed-off-by: Micah Morton <mortonm@chromium.org>
This commit is contained in:
Thomas Cedeno 2020-06-09 10:22:13 -07:00 committed by Micah Morton
parent 3d77e6a880
commit 39030e1351
5 changed files with 40 additions and 1 deletions
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2
include/linux/lsm_hook_defs.h
View File

@ -190,6 +190,8 @@ LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
loff_t size, enum kernel_read_file_id id)
LSM_HOOK(int, 0, task_fix_setuid, struct cred *new, const struct cred *old,
int flags)
LSM_HOOK(int, 0, task_fix_setgid, struct cred *new, const struct cred * old,
int flags)
LSM_HOOK(int, 0, task_setpgid, struct task_struct *p, pid_t pgid)
LSM_HOOK(int, 0, task_getpgid, struct task_struct *p)
LSM_HOOK(int, 0, task_getsid, struct task_struct *p)

9
include/linux/lsm_hooks.h
View File

@ -651,6 +651,15 @@
* @old is the set of credentials that are being replaces
* @flags contains one of the LSM_SETID_* values.
* Return 0 on success.
* @task_fix_setgid:
* Update the module's state after setting one or more of the group
* identity attributes of the current process. The @flags parameter
* indicates which of the set*gid system calls invoked this hook.
* @new is the set of credentials that will be installed. Modifications
* should be made to this rather than to @current->cred.
* @old is the set of credentials that are being replaced.
* @flags contains one of the LSM_SETID_* values.
* Return 0 on success.
* @task_setpgid:
* Check permission before setting the process group identifier of the
* process @p to @pgid.

9
include/linux/security.h
View File

@ -389,6 +389,8 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
enum kernel_read_file_id id);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags);
int security_task_fix_setgid(struct cred *new, const struct cred *old,
int flags);
int security_task_setpgid(struct task_struct *p, pid_t pgid);
int security_task_getpgid(struct task_struct *p);
int security_task_getsid(struct task_struct *p);
@ -1027,6 +1029,13 @@ static inline int security_task_fix_setuid(struct cred *new,
return cap_task_fix_setuid(new, old, flags);
}
static inline int security_task_fix_setgid(struct cred *new,
const struct cred *old,
int flags)
{
return 0;
}
static inline int security_task_setpgid(struct task_struct *p, pid_t pgid)
{
return 0;

15
kernel/sys.c
View File

@ -393,6 +393,10 @@ long __sys_setregid(gid_t rgid, gid_t egid)
new->sgid = new->egid;
new->fsgid = new->egid;
retval = security_task_fix_setgid(new, old, LSM_SETID_RE);
if (retval < 0)
goto error;
return commit_creds(new);
error:
@ -435,6 +439,10 @@ long __sys_setgid(gid_t gid)
else
goto error;
retval = security_task_fix_setgid(new, old, LSM_SETID_ID);
if (retval < 0)
goto error;
return commit_creds(new);
error:
@ -756,6 +764,10 @@ long __sys_setresgid(gid_t rgid, gid_t egid, gid_t sgid)
new->sgid = ksgid;
new->fsgid = new->egid;
retval = security_task_fix_setgid(new, old, LSM_SETID_RES);
if (retval < 0)
goto error;
return commit_creds(new);
error:
@ -862,7 +874,8 @@ long __sys_setfsgid(gid_t gid)
ns_capable(old->user_ns, CAP_SETGID)) {
if (!gid_eq(kgid, old->fsgid)) {
new->fsgid = kgid;
goto change_okay;
if (security_task_fix_setgid(new,old,LSM_SETID_FS) == 0)
goto change_okay;
}
}

6
security/security.c
View File

@ -1685,6 +1685,12 @@ int security_task_fix_setuid(struct cred *new, const struct cred *old,
return call_int_hook(task_fix_setuid, 0, new, old, flags);
}
int security_task_fix_setgid(struct cred *new, const struct cred *old,
int flags)
{
return call_int_hook(task_fix_setgid, 0, new, old, flags);
}
int security_task_setpgid(struct task_struct *p, pid_t pgid)
{
return call_int_hook(task_setpgid, 0, p, pgid);