Re: [PATCH v3 1/2] ima: Align ima_file_mmap() parameters with mmap_file LSM hook

[Stefan Berger <stefanb@linux.ibm.com>]

On 1/26/23 11:38, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
> 
> Commit 98de59bfe4b2f ("take calculation of final prot in
> security_mmap_file() into a helper") moved the code to update prot, to be
> the actual protections applied to the kernel, to a new helper called
> mmap_prot().
> 
> However, while without the helper ima_file_mmap() was getting the updated
> prot, with the helper ima_file_mmap() gets the original prot, which
> contains the protections requested by the application.
> 
> A possible consequence of this change is that, if an application calls
> mmap() with only PROT_READ, and the kernel applies PROT_EXEC in addition,
> that application would have access to executable memory without having this
> event recorded in the IMA measurement list. This situation would occur for
> example if the application, before mmap(), calls the personality() system
> call with READ_IMPLIES_EXEC as the first argument.
> 
> Align ima_file_mmap() parameters with those of the mmap_file LSM hook, so
> that IMA can receive both the requested prot and the final prot. Since the
> requested protections are stored in a new variable, and the final
> protections are stored in the existing variable, this effectively restores
> the original behavior of the MMAP_CHECK hook.
> 
And flags is being passed in preparation for IMA to meet the interface
requirements of the LSM hooks - I suppose in preparation for IMA to become an LSM.

> Cc: stable@vger.kernel.org
> Fixes: 98de59bfe4b2 ("take calculation of final prot in security_mmap_file() into a helper")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

> ---
>   include/linux/ima.h               | 6 ++++--
>   security/integrity/ima/ima_main.c | 7 +++++--
>   security/security.c               | 7 ++++---
>   3 files changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 5a0b2a285a18..d79fee67235e 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -21,7 +21,8 @@ extern int ima_file_check(struct file *file, int mask);
>   extern void ima_post_create_tmpfile(struct user_namespace *mnt_userns,
>   				    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_mmap(struct file *file, unsigned long reqprot,
> +			 unsigned long prot, unsigned long flags);
>   extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
>   extern int ima_load_data(enum kernel_load_data_id id, bool contents);
>   extern int ima_post_load_data(char *buf, loff_t size,
> @@ -76,7 +77,8 @@ static inline void ima_file_free(struct file *file)
>   	return;
>   }
>   
> -static inline int ima_file_mmap(struct file *file, unsigned long prot)
> +static inline int ima_file_mmap(struct file *file, unsigned long reqprot,
> +				unsigned long prot, unsigned long flags)
>   {
>   	return 0;
>   }
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 377300973e6c..f48f4e694921 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -397,7 +397,9 @@ static int process_measurement(struct file *file, const struct cred *cred,
>   /**
>    * ima_file_mmap - based on policy, collect/store measurement.
>    * @file: pointer to the file to be measured (May be NULL)
> - * @prot: contains the protection that will be applied by the kernel.
> + * @reqprot: protection requested by the application
> + * @prot: protection that will be applied by the kernel
> + * @flags: operational flags
>    *
>    * Measure files being mmapped executable based on the ima_must_measure()
>    * policy decision.
> @@ -405,7 +407,8 @@ static int process_measurement(struct file *file, const struct cred *cred,
>    * On success return 0.  On integrity appraisal error, assuming the file
>    * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
>    */
> -int ima_file_mmap(struct file *file, unsigned long prot)
> +int ima_file_mmap(struct file *file, unsigned long reqprot,
> +		  unsigned long prot, unsigned long flags)
>   {
>   	u32 secid;
>   
> diff --git a/security/security.c b/security/security.c
> index d1571900a8c7..174afa4fad81 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1661,12 +1661,13 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
>   int security_mmap_file(struct file *file, unsigned long prot,
>   			unsigned long flags)
>   {
> +	unsigned long prot_adj = mmap_prot(file, prot);
>   	int ret;
> -	ret = call_int_hook(mmap_file, 0, file, prot,
> -					mmap_prot(file, prot), flags);
> +
> +	ret = call_int_hook(mmap_file, 0, file, prot, prot_adj, flags);
>   	if (ret)
>   		return ret;
> -	return ima_file_mmap(file, prot);
> +	return ima_file_mmap(file, prot, prot_adj, flags);
>   }
>   
>   int security_mmap_addr(unsigned long addr)