[PATCH] Open a new file instance if no read permissions on files

[PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues]

Open a new file instance as opposed to changing file->f_mode when
the file is not readable.

This is done to accomodate overlayfs stacked file operations change. The
real struct file is hidden behind the overlays struct file. So, any
file->f_mode manipulations are not reflected on the real struct file.
Open the file again, read andcalculate the hash.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 7e7e7e7c250a..3848cf208792 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -210,7 +210,7 @@ static int ima_calc_file_hash_atfm(struct file *file,
 {
 	loff_t i_size, offset;
 	char *rbuf[2] = { NULL, };
-	int rc, read = 0, rbuf_len, active = 0, ahash_rc = 0;
+	int rc, rbuf_len, active = 0, ahash_rc = 0;
 	struct ahash_request *req;
 	struct scatterlist sg[1];
 	struct crypto_wait wait;
@@ -257,11 +257,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
 					  &rbuf_size[1], 0);
 	}
 
-	if (!(file->f_mode & FMODE_READ)) {
-		file->f_mode |= FMODE_READ;
-		read = 1;
-	}
-
 	for (offset = 0; offset < i_size; offset += rbuf_len) {
 		if (!rbuf[1] && offset) {
 			/* Not using two buffers, and it is not the first
@@ -300,8 +295,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
 	/* wait for the last update request to complete */
 	rc = ahash_wait(ahash_rc, &wait);
 out3:
-	if (read)
-		file->f_mode &= ~FMODE_READ;
 	ima_free_pages(rbuf[0], rbuf_size[0]);
 	ima_free_pages(rbuf[1], rbuf_size[1]);
 out2:
@@ -336,7 +329,7 @@ static int ima_calc_file_hash_tfm(struct file *file,
 {
 	loff_t i_size, offset = 0;
 	char *rbuf;
-	int rc, read = 0;
+	int rc;
 	SHASH_DESC_ON_STACK(shash, tfm);
 
 	shash->tfm = tfm;
@@ -357,11 +350,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
 	if (!rbuf)
 		return -ENOMEM;
 
-	if (!(file->f_mode & FMODE_READ)) {
-		file->f_mode |= FMODE_READ;
-		read = 1;
-	}
-
 	while (offset < i_size) {
 		int rbuf_len;
 
@@ -378,8 +366,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
 		if (rc)
 			break;
 	}
-	if (read)
-		file->f_mode &= ~FMODE_READ;
 	kfree(rbuf);
 out:
 	if (!rc)
@@ -419,7 +405,7 @@ static int ima_calc_file_shash(struct file *file, struct ima_digest_data *hash)
 int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 {
 	loff_t i_size;
-	int rc;
+	int read = 0, rc;
 
 	/*
 	 * For consistency, fail file's opened with the O_DIRECT flag on
@@ -431,15 +417,29 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 		return -EINVAL;
 	}
 
+	if (!(file->f_mode & FMODE_READ)) {
+		struct file *f;
+		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
+		f = dentry_open(&file->f_path, flags, file->f_cred);
+		if (IS_ERR(f))
+			return PTR_ERR(f);
+		read = 1;
+		file = f;
+	}
+
 	i_size = i_size_read(file_inode(file));
 
 	if (ima_ahash_minsize && i_size >= ima_ahash_minsize) {
 		rc = ima_calc_file_ahash(file, hash);
 		if (!rc)
-			return 0;
+			goto out;
 	}
 
-	return ima_calc_file_shash(file, hash);
+	rc = ima_calc_file_shash(file, hash);
+out:
+	if (read)
+		fput(file);
+	return rc;
 }
 
 /*

-- 
Goldwyn

Re: [PATCH] Open a new file instance if no read permissions on files

[Mimi Zohar]

On Fri, 2018-10-05 at 16:42 -0500, Goldwyn Rodrigues wrote:
> Open a new file instance as opposed to changing file->f_mode when
> the file is not readable.
> 
> This is done to accomodate overlayfs stacked file operations change. The
> real struct file is hidden behind the overlays struct file. So, any
> file->f_mode manipulations are not reflected on the real struct file.
> Open the file again, read andcalculate the hash.
> 
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> 
> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
> index 7e7e7e7c250a..3848cf208792 100644
> --- a/security/integrity/ima/ima_crypto.c
> +++ b/security/integrity/ima/ima_crypto.c
> @@ -210,7 +210,7 @@ static int ima_calc_file_hash_atfm(struct file *file,
>  {
>  	loff_t i_size, offset;
>  	char *rbuf[2] = { NULL, };
> -	int rc, read = 0, rbuf_len, active = 0, ahash_rc = 0;
> +	int rc, rbuf_len, active = 0, ahash_rc = 0;
>  	struct ahash_request *req;
>  	struct scatterlist sg[1];
>  	struct crypto_wait wait;
> @@ -257,11 +257,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
>  					  &rbuf_size[1], 0);
>  	}
>  
> -	if (!(file->f_mode & FMODE_READ)) {
> -		file->f_mode |= FMODE_READ;
> -		read = 1;
> -	}
> -
>  	for (offset = 0; offset < i_size; offset += rbuf_len) {
>  		if (!rbuf[1] && offset) {
>  			/* Not using two buffers, and it is not the first
> @@ -300,8 +295,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
>  	/* wait for the last update request to complete */
>  	rc = ahash_wait(ahash_rc, &wait);
>  out3:
> -	if (read)
> -		file->f_mode &= ~FMODE_READ;
>  	ima_free_pages(rbuf[0], rbuf_size[0]);
>  	ima_free_pages(rbuf[1], rbuf_size[1]);
>  out2:
> @@ -336,7 +329,7 @@ static int ima_calc_file_hash_tfm(struct file *file,
>  {
>  	loff_t i_size, offset = 0;
>  	char *rbuf;
> -	int rc, read = 0;
> +	int rc;
>  	SHASH_DESC_ON_STACK(shash, tfm);
>  
>  	shash->tfm = tfm;
> @@ -357,11 +350,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
>  	if (!rbuf)
>  		return -ENOMEM;
>  
> -	if (!(file->f_mode & FMODE_READ)) {
> -		file->f_mode |= FMODE_READ;
> -		read = 1;
> -	}
> -
>  	while (offset < i_size) {
>  		int rbuf_len;
>  
> @@ -378,8 +366,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
>  		if (rc)
>  			break;
>  	}
> -	if (read)
> -		file->f_mode &= ~FMODE_READ;
>  	kfree(rbuf);
>  out:
>  	if (!rc)
> @@ -419,7 +405,7 @@ static int ima_calc_file_shash(struct file *file, struct ima_digest_data *hash)
>  int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
>  {
>  	loff_t i_size;
> -	int rc;
> +	int read = 0, rc;
>  
>  	/*
>  	 * For consistency, fail file's opened with the O_DIRECT flag on
> @@ -431,15 +417,29 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
>  		return -EINVAL;
>  	}
>  
> +	if (!(file->f_mode & FMODE_READ)) {
> +		struct file *f;

I would define "struct file *f = file" above, at the beginning of
function, and "free(f)" below, without modifying "file".

> +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);

Doesn't O_RDONLY need to be added?
Please fix the line length.


> +		f = dentry_open(&file->f_path, flags, file->f_cred);
> +		if (IS_ERR(f))
> +			return PTR_ERR(f);
> +		read = 1;
> +		file = f;

With the above change, no need to modify "file".

Mimi

> +	}
> +
>  	i_size = i_size_read(file_inode(file));
>  
>  	if (ima_ahash_minsize && i_size >= ima_ahash_minsize) {
>  		rc = ima_calc_file_ahash(file, hash);
>  		if (!rc)
> -			return 0;
> +			goto out;
>  	}
>  
> -	return ima_calc_file_shash(file, hash);
> +	rc = ima_calc_file_shash(file, hash);
> +out:
> +	if (read)
> +		fput(file);
> +	return rc;
>  }
>  
>  /*
> 

Re: [PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues]

On 21:01 06/10, Mimi Zohar wrote:
> On Fri, 2018-10-05 at 16:42 -0500, Goldwyn Rodrigues wrote:
> > Open a new file instance as opposed to changing file->f_mode when
> > the file is not readable.
> > 
> > This is done to accomodate overlayfs stacked file operations change. The
> > real struct file is hidden behind the overlays struct file. So, any
> > file->f_mode manipulations are not reflected on the real struct file.
> > Open the file again, read andcalculate the hash.
> > 
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > 
> > diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
> > index 7e7e7e7c250a..3848cf208792 100644
> > --- a/security/integrity/ima/ima_crypto.c
> > +++ b/security/integrity/ima/ima_crypto.c
> > @@ -210,7 +210,7 @@ static int ima_calc_file_hash_atfm(struct file *file,
> >  {
> >  	loff_t i_size, offset;
> >  	char *rbuf[2] = { NULL, };
> > -	int rc, read = 0, rbuf_len, active = 0, ahash_rc = 0;
> > +	int rc, rbuf_len, active = 0, ahash_rc = 0;
> >  	struct ahash_request *req;
> >  	struct scatterlist sg[1];
> >  	struct crypto_wait wait;
> > @@ -257,11 +257,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
> >  					  &rbuf_size[1], 0);
> >  	}
> >  
> > -	if (!(file->f_mode & FMODE_READ)) {
> > -		file->f_mode |= FMODE_READ;
> > -		read = 1;
> > -	}
> > -
> >  	for (offset = 0; offset < i_size; offset += rbuf_len) {
> >  		if (!rbuf[1] && offset) {
> >  			/* Not using two buffers, and it is not the first
> > @@ -300,8 +295,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
> >  	/* wait for the last update request to complete */
> >  	rc = ahash_wait(ahash_rc, &wait);
> >  out3:
> > -	if (read)
> > -		file->f_mode &= ~FMODE_READ;
> >  	ima_free_pages(rbuf[0], rbuf_size[0]);
> >  	ima_free_pages(rbuf[1], rbuf_size[1]);
> >  out2:
> > @@ -336,7 +329,7 @@ static int ima_calc_file_hash_tfm(struct file *file,
> >  {
> >  	loff_t i_size, offset = 0;
> >  	char *rbuf;
> > -	int rc, read = 0;
> > +	int rc;
> >  	SHASH_DESC_ON_STACK(shash, tfm);
> >  
> >  	shash->tfm = tfm;
> > @@ -357,11 +350,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
> >  	if (!rbuf)
> >  		return -ENOMEM;
> >  
> > -	if (!(file->f_mode & FMODE_READ)) {
> > -		file->f_mode |= FMODE_READ;
> > -		read = 1;
> > -	}
> > -
> >  	while (offset < i_size) {
> >  		int rbuf_len;
> >  
> > @@ -378,8 +366,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
> >  		if (rc)
> >  			break;
> >  	}
> > -	if (read)
> > -		file->f_mode &= ~FMODE_READ;
> >  	kfree(rbuf);
> >  out:
> >  	if (!rc)
> > @@ -419,7 +405,7 @@ static int ima_calc_file_shash(struct file *file, struct ima_digest_data *hash)
> >  int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
> >  {
> >  	loff_t i_size;
> > -	int rc;
> > +	int read = 0, rc;
> >  
> >  	/*
> >  	 * For consistency, fail file's opened with the O_DIRECT flag on
> > @@ -431,15 +417,29 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
> >  		return -EINVAL;
> >  	}
> >  
> > +	if (!(file->f_mode & FMODE_READ)) {
> > +		struct file *f;
> 
> I would define "struct file *f = file" above, at the beginning of
> function, and "free(f)" below, without modifying "file".

I suppose you mean fput(f).
Okay, if it makes code more understandable.

> 
> > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> 
> Doesn't O_RDONLY need to be added?

No. O_RDONLY is zero. But I think I should add it for readability. The
compiler will optimize it eventually.

> Please fix the line length.
> 
> 
> > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > +		if (IS_ERR(f))
> > +			return PTR_ERR(f);
> > +		read = 1;
> > +		file = f;
> 
> With the above change, no need to modify "file".
> 
> Mimi
> 
> > +	}
> > +
> >  	i_size = i_size_read(file_inode(file));
> >  
> >  	if (ima_ahash_minsize && i_size >= ima_ahash_minsize) {
> >  		rc = ima_calc_file_ahash(file, hash);
> >  		if (!rc)
> > -			return 0;
> > +			goto out;
> >  	}
> >  
> > -	return ima_calc_file_shash(file, hash);
> > +	rc = ima_calc_file_shash(file, hash);
> > +out:
> > +	if (read)
> > +		fput(file);
> > +	return rc;
> >  }
> >  
> >  /*
> > 
> 

-- 
Goldwyn

Re: [PATCH] Open a new file instance if no read permissions on files

[Mimi Zohar]

On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:

> 
> > >  
> > > +	if (!(file->f_mode & FMODE_READ)) {
> > > +		struct file *f;
> > 
> > I would define "struct file *f = file" above, at the beginning of
> > function, and "free(f)" below, without modifying "file".
> 
> I suppose you mean fput(f).

yes

> Okay, if it makes code more understandable.

Thanks
> 
> > 
> > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > 
> > Doesn't O_RDONLY need to be added?
> 
> No. O_RDONLY is zero. But I think I should add it for readability. The
> compiler will optimize it eventually.
> 
> > Please fix the line length.
> > 
> > 
> > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > +		if (IS_ERR(f))
> > > +			return PTR_ERR(f);

It's late in the release cycle to be making this change.  Would it
make sense for now to fallback to modifying the original file
descriptor on failure and emit a message?

Mimi


> > > +		read = 1;
> > > +		file = f;
> > 
> > With the above change, no need to modify "file".
> 

Re: [PATCH] Open a new file instance if no read permissions on files

[Mimi Zohar]

On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:

> 
> > >  
> > > +	if (!(file->f_mode & FMODE_READ)) {
> > > +		struct file *f;
> > 
> > I would define "struct file *f = file" above, at the beginning of
> > function, and "free(f)" below, without modifying "file".
> 
> I suppose you mean fput(f).

yes

> Okay, if it makes code more understandable.

Thanks
> 
> > 
> > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > 
> > Doesn't O_RDONLY need to be added?
> 
> No. O_RDONLY is zero. But I think I should add it for readability. The
> compiler will optimize it eventually.
> 
> > Please fix the line length.
> > 
> > 
> > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > +		if (IS_ERR(f))
> > > +			return PTR_ERR(f);

It's late in the release cycle to be making this change.  Would it
make sense for now to fallback to modifying the original file
descriptor on failure and emit a message?

Mimi


> > > +		read = 1;
> > > +		file = f;
> > 
> > With the above change, no need to modify "file".
> 

Re: [PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues]

On  9:27 08/10, Mimi Zohar wrote:
> On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:
> 
> > 
> > > >  
> > > > +	if (!(file->f_mode & FMODE_READ)) {
> > > > +		struct file *f;
> > > 
> > > I would define "struct file *f = file" above, at the beginning of
> > > function, and "free(f)" below, without modifying "file".
> > 
> > I suppose you mean fput(f).
> 
> yes
> 
> > Okay, if it makes code more understandable.
> 
> Thanks
> > 
> > > 
> > > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > > 
> > > Doesn't O_RDONLY need to be added?
> > 
> > No. O_RDONLY is zero. But I think I should add it for readability. The
> > compiler will optimize it eventually.
> > 
> > > Please fix the line length.
> > > 
> > > 
> > > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > > +		if (IS_ERR(f))
> > > > +			return PTR_ERR(f);
> 
> It's late in the release cycle to be making this change. �Would it
> make sense for now to fallback to modifying the original file
> descriptor on failure and emit a message?

Yes, perhaps and it may still succeed. Won't it be misleading if it does?
Would ima_update_xattr() be a good place? Not sure if it would spew too
many messages if there is an issue. I am all in for modifying the
original file->f_flags on failure. Just not sure about the error
message.

Currently, when we perform IMA hash calculation on a O_WRONLY file with
overlayfs, there is no error in dmesg. Just EACCES on the _next_ write
which makes it difficult to conclude whats wrong.

-- 
Goldwyn

Re: [PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues]

On  9:27 08/10, Mimi Zohar wrote:
> On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:
> 
> > 
> > > >  
> > > > +	if (!(file->f_mode & FMODE_READ)) {
> > > > +		struct file *f;
> > > 
> > > I would define "struct file *f = file" above, at the beginning of
> > > function, and "free(f)" below, without modifying "file".
> > 
> > I suppose you mean fput(f).
> 
> yes
> 
> > Okay, if it makes code more understandable.
> 
> Thanks
> > 
> > > 
> > > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > > 
> > > Doesn't O_RDONLY need to be added?
> > 
> > No. O_RDONLY is zero. But I think I should add it for readability. The
> > compiler will optimize it eventually.
> > 
> > > Please fix the line length.
> > > 
> > > 
> > > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > > +		if (IS_ERR(f))
> > > > +			return PTR_ERR(f);
> 
> It's late in the release cycle to be making this change.  Would it
> make sense for now to fallback to modifying the original file
> descriptor on failure and emit a message?

Yes, perhaps and it may still succeed. Won't it be misleading if it does?
Would ima_update_xattr() be a good place? Not sure if it would spew too
many messages if there is an issue. I am all in for modifying the
original file->f_flags on failure. Just not sure about the error
message.

Currently, when we perform IMA hash calculation on a O_WRONLY file with
overlayfs, there is no error in dmesg. Just EACCES on the _next_ write
which makes it difficult to conclude whats wrong.

-- 
Goldwyn

Re: [PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues]

On  9:27 08/10, Mimi Zohar wrote:
> On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:
> 
> > 
> > > >  
> > > > +	if (!(file->f_mode & FMODE_READ)) {
> > > > +		struct file *f;
> > > 
> > > I would define "struct file *f = file" above, at the beginning of
> > > function, and "free(f)" below, without modifying "file".
> > 
> > I suppose you mean fput(f).
> 
> yes
> 
> > Okay, if it makes code more understandable.
> 
> Thanks
> > 
> > > 
> > > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > > 
> > > Doesn't O_RDONLY need to be added?
> > 
> > No. O_RDONLY is zero. But I think I should add it for readability. The
> > compiler will optimize it eventually.
> > 
> > > Please fix the line length.
> > > 
> > > 
> > > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > > +		if (IS_ERR(f))
> > > > +			return PTR_ERR(f);
> 
> It's late in the release cycle to be making this change.  Would it
> make sense for now to fallback to modifying the original file
> descriptor on failure and emit a message?

Yes, perhaps and it may still succeed. Won't it be misleading if it does?
Would ima_update_xattr() be a good place? Not sure if it would spew too
many messages if there is an issue. I am all in for modifying the
original file->f_flags on failure. Just not sure about the error
message.

Currently, when we perform IMA hash calculation on a O_WRONLY file with
overlayfs, there is no error in dmesg. Just EACCES on the _next_ write
which makes it difficult to conclude whats wrong.

-- 
Goldwyn

Re: [PATCH] Open a new file instance if no read permissions on files

[Mimi Zohar]

On Mon, 2018-10-08 at 10:30 -0500, Goldwyn Rodrigues wrote:
> On  9:27 08/10, Mimi Zohar wrote:
> > On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:
> > 
> > > 
> > > > >  
> > > > > +	if (!(file->f_mode & FMODE_READ)) {
> > > > > +		struct file *f;
> > > > 
> > > > I would define "struct file *f = file" above, at the beginning of
> > > > function, and "free(f)" below, without modifying "file".
> > > 
> > > I suppose you mean fput(f).
> > 
> > yes
> > 
> > > Okay, if it makes code more understandable.
> > 
> > Thanks
> > > 
> > > > 
> > > > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > > > 
> > > > Doesn't O_RDONLY need to be added?
> > > 
> > > No. O_RDONLY is zero. But I think I should add it for readability. The
> > > compiler will optimize it eventually.
> > > 
> > > > Please fix the line length.
> > > > 
> > > > 
> > > > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > > > +		if (IS_ERR(f))
> > > > > +			return PTR_ERR(f);
> > 
> > It's late in the release cycle to be making this change.  Would it
> > make sense for now to fallback to modifying the original file
> > descriptor on failure and emit a message?
> 
> Yes, perhaps and it may still succeed. Won't it be misleading if it does?
> Would ima_update_xattr() be a good place? Not sure if it would spew too
> many messages if there is an issue. I am all in for modifying the
> original file->f_flags on failure. Just not sure about the error
> message.

The message should be an indication that the dentry_open() failed.  So
it needs to be in ima_calc_file_hash.  Perhaps use either
pr_info_ratelimited or even pr_info_once() to limit the number of
messages.

> Currently, when we perform IMA hash calculation on a O_WRONLY file with
> overlayfs, there is no error in dmesg. Just EACCES on the _next_ write
> which makes it difficult to conclude whats wrong.

There should be an AUDIT_INTEGRITY_DATA message emitted by
ima_collect_measurement().

Mimi

Re: [PATCH] Open a new file instance if no read permissions on files

[Mimi Zohar]

On Mon, 2018-10-08 at 10:30 -0500, Goldwyn Rodrigues wrote:
> On  9:27 08/10, Mimi Zohar wrote:
> > On Mon, 2018-10-08 at 07:14 -0500, Goldwyn Rodrigues wrote:
> > 
> > > 
> > > > >  
> > > > > +	if (!(file->f_mode & FMODE_READ)) {
> > > > > +		struct file *f;
> > > > 
> > > > I would define "struct file *f = file" above, at the beginning of
> > > > function, and "free(f)" below, without modifying "file".
> > > 
> > > I suppose you mean fput(f).
> > 
> > yes
> > 
> > > Okay, if it makes code more understandable.
> > 
> > Thanks
> > > 
> > > > 
> > > > > +		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
> > > > 
> > > > Doesn't O_RDONLY need to be added?
> > > 
> > > No. O_RDONLY is zero. But I think I should add it for readability. The
> > > compiler will optimize it eventually.
> > > 
> > > > Please fix the line length.
> > > > 
> > > > 
> > > > > +		f = dentry_open(&file->f_path, flags, file->f_cred);
> > > > > +		if (IS_ERR(f))
> > > > > +			return PTR_ERR(f);
> > 
> > It's late in the release cycle to be making this change.  Would it
> > make sense for now to fallback to modifying the original file
> > descriptor on failure and emit a message?
> 
> Yes, perhaps and it may still succeed. Won't it be misleading if it does?
> Would ima_update_xattr() be a good place? Not sure if it would spew too
> many messages if there is an issue. I am all in for modifying the
> original file->f_flags on failure. Just not sure about the error
> message.

The message should be an indication that the dentry_open() failed.  So
it needs to be in ima_calc_file_hash.  Perhaps use either
pr_info_ratelimited or even pr_info_once() to limit the number of
messages.

> Currently, when we perform IMA hash calculation on a O_WRONLY file with
> overlayfs, there is no error in dmesg. Just EACCES on the _next_ write
> which makes it difficult to conclude whats wrong.

There should be an AUDIT_INTEGRITY_DATA message emitted by
ima_collect_measurement().

Mimi