[2/5] ext2: preserve i_mode if ext2_set_acl() fails

Submitted by Ernesto A. Fernández on July 12, 2017, 9:54 a.m.

Details

Message ID 099e3ef2bf3a9ab2a1d545b65ba15fad359f2c03.1499805487.git.ernesto.mnd.fernandez@gmail.com
State New
Headers show

Commit Message

Ernesto A. Fernández July 12, 2017, 9:54 a.m.
When changing a file's acl mask, ext2_set_acl() will first set the group
bits of i_mode to the value of the mask, and only then set the actual
extended attribute representing the new acl.

If the second part fails (due to lack of space, for example) and the file
had no acl attribute to begin with, the system will from now on assume
that the mask permission bits are actual group permission bits, potentially
granting access to the wrong users.

Prevent this by only changing the inode mode after the acl has been set.

Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
---
A line in acl.c is too long, and checkpatch.pl complains about it when run
against this patch. In case it matters, the next patch will fix that.

 fs/ext2/acl.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

Comments

Jan Kara July 17, 2017, 4:33 p.m.
On Wed 12-07-17 06:54:19, Ernesto A. Fernández wrote:
> When changing a file's acl mask, ext2_set_acl() will first set the group
> bits of i_mode to the value of the mask, and only then set the actual
> extended attribute representing the new acl.
> 
> If the second part fails (due to lack of space, for example) and the file
> had no acl attribute to begin with, the system will from now on assume
> that the mask permission bits are actual group permission bits, potentially
> granting access to the wrong users.
> 
> Prevent this by only changing the inode mode after the acl has been set.
> 
> Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>

Thanks for the patch! I have rebased it on top of the fix in that area that
is sitting in my tree and merged it to my tree.

								Honza

> ---
> A line in acl.c is too long, and checkpatch.pl complains about it when run
> against this patch. In case it matters, the next patch will fix that.
> 
>  fs/ext2/acl.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
> index 79dafa7..4e04b7e 100644
> --- a/fs/ext2/acl.c
> +++ b/fs/ext2/acl.c
> @@ -185,16 +185,17 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	void *value = NULL;
>  	size_t size = 0;
>  	int error;
> +	int update_mode = 0;
> +	umode_t mode = inode->i_mode;
>  
>  	switch(type) {
>  		case ACL_TYPE_ACCESS:
>  			name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
>  			if (acl) {
> -				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
> +				error = posix_acl_update_mode(inode, &mode, &acl);
>  				if (error)
>  					return error;
> -				inode->i_ctime = current_time(inode);
> -				mark_inode_dirty(inode);
> +				update_mode = 1;
>  			}
>  			break;
>  
> @@ -216,8 +217,14 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	error = ext2_xattr_set(inode, name_index, "", value, size, 0);
>  
>  	kfree(value);
> -	if (!error)
> +	if (!error) {
>  		set_cached_acl(inode, type, acl);
> +		if (update_mode) {
> +			inode->i_mode = mode;
> +			inode->i_ctime = current_time(inode);
> +			mark_inode_dirty(inode);
> +		}
> +	}
>  	return error;
>  }
>  
> -- 
> 2.1.4
> 
>

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diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
index 79dafa7..4e04b7e 100644
--- a/fs/ext2/acl.c
+++ b/fs/ext2/acl.c
@@ -185,16 +185,17 @@  ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	void *value = NULL;
 	size_t size = 0;
 	int error;
+	int update_mode = 0;
+	umode_t mode = inode->i_mode;
 
 	switch(type) {
 		case ACL_TYPE_ACCESS:
 			name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
 			if (acl) {
-				error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+				error = posix_acl_update_mode(inode, &mode, &acl);
 				if (error)
 					return error;
-				inode->i_ctime = current_time(inode);
-				mark_inode_dirty(inode);
+				update_mode = 1;
 			}
 			break;
 
@@ -216,8 +217,14 @@  ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	error = ext2_xattr_set(inode, name_index, "", value, size, 0);
 
 	kfree(value);
-	if (!error)
+	if (!error) {
 		set_cached_acl(inode, type, acl);
+		if (update_mode) {
+			inode->i_mode = mode;
+			inode->i_ctime = current_time(inode);
+			mark_inode_dirty(inode);
+		}
+	}
 	return error;
 }