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ima: verify mprotect change is consistent with mmap policy

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Files can be mmap'ed read/write and later changed to execute to circumvent
IMA's mmap appraise policy rules.  Due to locking issues (mmap semaphore
would be taken prior to i_mutex), files can not be measured or appraised at
this point.  Eliminate this integrity gap, by denying the mprotect
PROT_EXECUTE change, if an mmap appraise policy rule exists.

On mprotect change success, return 0.  On failure, return -EACESS.

Reviewed-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Mimi Zohar 2020-05-03 01:00:02 -04:00
parent 0c4395fb2a
commit 8eb613c0b8
3 changed files with 64 additions and 1 deletions
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7
include/linux/ima.h
View File

@ -18,6 +18,7 @@ extern int ima_file_check(struct file *file, int mask);
extern void ima_post_create_tmpfile(struct inode *inode);
extern void ima_file_free(struct file *file);
extern int ima_file_mmap(struct file *file, unsigned long prot);
extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
extern int ima_load_data(enum kernel_load_data_id id);
extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
@ -70,6 +71,12 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)
return 0;
}
static inline int ima_file_mprotect(struct vm_area_struct *vma,
unsigned long prot)
{
return 0;
}
static inline int ima_load_data(enum kernel_load_data_id id)
{
return 0;

51
security/integrity/ima/ima_main.c
View File

@ -393,6 +393,57 @@ int ima_file_mmap(struct file *file, unsigned long prot)
return 0;
}
/**
* ima_file_mprotect - based on policy, limit mprotect change
* @prot: contains the protection that will be applied by the kernel.
*
* Files can be mmap'ed read/write and later changed to execute to circumvent
* IMA's mmap appraisal policy rules. Due to locking issues (mmap semaphore
* would be taken before i_mutex), files can not be measured or appraised at
* this point. Eliminate this integrity gap by denying the mprotect
* PROT_EXECUTE change, if an mmap appraise policy rule exists.
*
* On mprotect change success, return 0. On failure, return -EACESS.
*/
int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
{
struct ima_template_desc *template;
struct file *file = vma->vm_file;
char filename[NAME_MAX];
char *pathbuf = NULL;
const char *pathname = NULL;
struct inode *inode;
int result = 0;
int action;
u32 secid;
int pcr;
/* Is mprotect making an mmap'ed file executable? */
if (!vma->vm_file || !(prot & PROT_EXEC) || (vma->vm_flags & VM_EXEC))
return 0;
security_task_getsecid(current, &secid);
inode = file_inode(vma->vm_file);
action = ima_get_action(inode, current_cred(), secid, MAY_EXEC,
MMAP_CHECK, &pcr, &template, 0);
/* Is the mmap'ed file in policy? */
if (!(action & (IMA_MEASURE | IMA_APPRAISE_SUBMASK)))
return 0;
if (action & IMA_APPRAISE_SUBMASK)
result = -EPERM;
file = vma->vm_file;
pathname = ima_d_path(&file->f_path, &pathbuf, filename);
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, pathname,
"collect_data", "failed-mprotect", result, 0);
if (pathbuf)
__putname(pathbuf);
return result;
}
/**
* ima_bprm_check - based on policy, collect/store measurement.
* @bprm: contains the linux_binprm structure

7
security/security.c
View File

@ -1512,7 +1512,12 @@ int security_mmap_addr(unsigned long addr)
int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
unsigned long prot)
{
return call_int_hook(file_mprotect, 0, vma, reqprot, prot);
int ret;
ret = call_int_hook(file_mprotect, 0, vma, reqprot, prot);
if (ret)
return ret;
return ima_file_mprotect(vma, prot);
}
int security_file_lock(struct file *file, unsigned int cmd)