posix_acl: Clear SGID bit when setting file permissions

commit 073931017b49d9458aa351605b43a7e34598caef upstream.

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
[bwh: Backported to 3.2:
 - Drop changes to ceph, f2fs, hfsplus, orangefs
 - Use capable() instead of capable_wrt_inode_uidgid()
 - Update ext3 and generic_acl.c as well
 - In gfs2, jfs, and xfs, take care to avoid leaking the allocated ACL if
   posix_acl_update_mode() determines it's not needed
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/9p/acl.c b/fs/9p/acl.c
index 9a1d426..a4188cf 100644 (file)
--- a/fs/9p/acl.c
+++ b/fs/9p/acl.c
@@ -319,32 +319,26 @@ static int v9fs_xattr_set_acl(struct dentry *dentry, const char *name,
        case ACL_TYPE_ACCESS:
                name = POSIX_ACL_XATTR_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       retval = posix_acl_equiv_mode(acl, &mode);
-                       if (retval < 0)
+                       struct iattr iattr;
+
+                       retval = posix_acl_update_mode(inode, &iattr.ia_mode, &acl);
+                       if (retval)
                                goto err_out;
-                       else {
-                               struct iattr iattr;
-                               if (retval == 0) {
-                                       /*
-                                        * ACL can be represented
-                                        * by the mode bits. So don't
-                                        * update ACL.
-                                        */
-                                       acl = NULL;
-                                       value = NULL;
-                                       size = 0;
-                               }
-                               /* Updte the mode bits */
-                               iattr.ia_mode = ((mode & S_IALLUGO) |
-                                                (inode->i_mode & ~S_IALLUGO));
-                               iattr.ia_valid = ATTR_MODE;
-                               /* FIXME should we update ctime ?
-                                * What is the following setxattr update the
-                                * mode ?
+                       if (!acl) {
+                               /*
+                                * ACL can be represented
+                                * by the mode bits. So don't
+                                * update ACL.
                                 */
-                               v9fs_vfs_setattr_dotl(dentry, &iattr);
+                               value = NULL;
+                               size = 0;
                        }
+                       iattr.ia_valid = ATTR_MODE;
+                       /* FIXME should we update ctime ?
+                        * What is the following setxattr update the
+                        * mode ?
+                        */
+                       v9fs_vfs_setattr_dotl(dentry, &iattr);
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index a1f6a1b..9f55b54 100644 (file)
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -118,11 +118,9 @@ static int btrfs_set_acl(struct btrfs_trans_handle *trans,
        case ACL_TYPE_ACCESS:
                name = POSIX_ACL_XATTR_ACCESS;
                if (acl) {
-                       ret = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (ret < 0)
+                       ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (ret)
                                return ret;
-                       if (ret == 0)
-                               acl = NULL;
                }
                ret = 0;
                break;

diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
index 35d6a3c..e38a9b6 100644 (file)
--- a/fs/ext2/acl.c
+++ b/fs/ext2/acl.c
@@ -194,15 +194,11 @@ ext2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
                case ACL_TYPE_ACCESS:
                        name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
                        if (acl) {
-                               error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                               if (error < 0)
+                               error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                               if (error)
                                        return error;
-                               else {
-                                       inode->i_ctime = CURRENT_TIME_SEC;
-                                       mark_inode_dirty(inode);
-                                       if (error == 0)
-                                               acl = NULL;
-                               }
+                               inode->i_ctime = CURRENT_TIME_SEC;
+                               mark_inode_dirty(inode);
                        }
                        break;
 

diff --git a/fs/ext3/acl.c b/fs/ext3/acl.c
index 3091f62..880d3d6 100644 (file)
--- a/fs/ext3/acl.c
+++ b/fs/ext3/acl.c
@@ -199,15 +199,11 @@ ext3_set_acl(handle_t *handle, struct inode *inode, int type,
                case ACL_TYPE_ACCESS:
                        name_index = EXT3_XATTR_INDEX_POSIX_ACL_ACCESS;
                        if (acl) {
-                               error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                               if (error < 0)
+                               error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                               if (error)
                                        return error;
-                               else {
-                                       inode->i_ctime = CURRENT_TIME_SEC;
-                                       ext3_mark_inode_dirty(handle, inode);
-                                       if (error == 0)
-                                               acl = NULL;
-                               }
+                               inode->i_ctime = CURRENT_TIME_SEC;
+                               ext3_mark_inode_dirty(handle, inode);
                        }
                        break;
 

diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
index 8535c45..5d419a4 100644 (file)
--- a/fs/ext4/acl.c
+++ b/fs/ext4/acl.c
@@ -198,15 +198,11 @@ ext4_set_acl(handle_t *handle, struct inode *inode, int type,
        case ACL_TYPE_ACCESS:
                name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
                if (acl) {
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (error)
                                return error;
-                       else {
-                               inode->i_ctime = ext4_current_time(inode);
-                               ext4_mark_inode_dirty(handle, inode);
-                               if (error == 0)
-                                       acl = NULL;
-                       }
+                       inode->i_ctime = ext4_current_time(inode);
+                       ext4_mark_inode_dirty(handle, inode);
                }
                break;
 

diff --git a/fs/generic_acl.c b/fs/generic_acl.c
index d0dddac..a3f3e70 100644 (file)
--- a/fs/generic_acl.c
+++ b/fs/generic_acl.c
@@ -86,16 +86,17 @@ generic_acl_set(struct dentry *dentry, const char *name, const void *value,
                if (error)
                        goto failed;
                switch (type) {
-               case ACL_TYPE_ACCESS:
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+               case ACL_TYPE_ACCESS: {
+                       struct posix_acl *saved_acl = acl;
+
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (acl == NULL)
+                               posix_acl_release(saved_acl);
+                       if (error)
                                goto failed;
                        inode->i_ctime = CURRENT_TIME;
-                       if (error == 0) {
-                               posix_acl_release(acl);
-                               acl = NULL;
-                       }
                        break;
+               }
                case ACL_TYPE_DEFAULT:
                        if (!S_ISDIR(inode->i_mode)) {
                                error = -EINVAL;

diff --git a/fs/gfs2/acl.c b/fs/gfs2/acl.c
index 65978d7..75f6085 100644 (file)
--- a/fs/gfs2/acl.c
+++ b/fs/gfs2/acl.c
@@ -277,16 +277,14 @@ static int gfs2_xattr_system_set(struct dentry *dentry, const char *name,
                goto out_release;
 
        if (type == ACL_TYPE_ACCESS) {
-               umode_t mode = inode->i_mode;
-               error = posix_acl_equiv_mode(acl, &mode);
+               struct posix_acl *saved_acl = acl;
+               umode_t mode;
 
-               if (error <= 0) {
-                       posix_acl_release(acl);
-                       acl = NULL;
-
-                       if (error < 0)
-                               return error;
-               }
+               error = posix_acl_update_mode(inode, &mode, &acl);
+               if (error || acl == NULL)
+                       posix_acl_release(saved_acl);
+               if (error)
+                       return error;
 
                error = gfs2_set_mode(inode, mode);
                if (error)

diff --git a/fs/jffs2/acl.c b/fs/jffs2/acl.c
index 926d020..d963e55 100644 (file)
--- a/fs/jffs2/acl.c
+++ b/fs/jffs2/acl.c
@@ -227,9 +227,10 @@ static int jffs2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
        case ACL_TYPE_ACCESS:
                xprefix = JFFS2_XPREFIX_ACL_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       rc = posix_acl_equiv_mode(acl, &mode);
-                       if (rc < 0)
+                       umode_t mode;
+
+                       rc = posix_acl_update_mode(inode, &mode, &acl);
+                       if (rc)
                                return rc;
                        if (inode->i_mode != mode) {
                                struct iattr attr;
@@ -241,8 +242,6 @@ static int jffs2_set_acl(struct inode *inode, int type, struct posix_acl *acl)
                                if (rc < 0)
                                        return rc;
                        }
-                       if (rc == 0)
-                               acl = NULL;
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c
index 26683e1..1078c93 100644 (file)
--- a/fs/jfs/xattr.c
+++ b/fs/jfs/xattr.c
@@ -693,9 +693,11 @@ static int can_set_system_xattr(struct inode *inode, const char *name,
                        return rc;
                }
                if (acl) {
-                       rc = posix_acl_equiv_mode(acl, &inode->i_mode);
+                       struct posix_acl *dummy = acl;
+
+                       rc = posix_acl_update_mode(inode, &inode->i_mode, &dummy);
                        posix_acl_release(acl);
-                       if (rc < 0) {
+                       if (rc) {
                                printk(KERN_ERR
                                       "posix_acl_equiv_mode returned %d\n",
                                       rc);

diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
index a721907..7e6e1f8 100644 (file)
--- a/fs/ocfs2/acl.c
+++ b/fs/ocfs2/acl.c
@@ -247,14 +247,11 @@ static int ocfs2_set_acl(handle_t *handle,
        case ACL_TYPE_ACCESS:
                name_index = OCFS2_XATTR_INDEX_POSIX_ACL_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       ret = posix_acl_equiv_mode(acl, &mode);
-                       if (ret < 0)
+                       umode_t mode;
+                       ret = posix_acl_update_mode(inode, &mode, &acl);
+                       if (ret)
                                return ret;
                        else {
-                               if (ret == 0)
-                                       acl = NULL;
-
                                ret = ocfs2_acl_set_mode(inode, di_bh,
                                                         handle, mode);
                                if (ret)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 6c70ab2..0ff2079 100644 (file)
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -341,6 +341,36 @@ static int posix_acl_create_masq(struct posix_acl *acl, umode_t *mode_p)
         return not_equiv;
 }
 
+/**
+ * posix_acl_update_mode  -  update mode in set_acl
+ *
+ * Update the file mode when setting an ACL: compute the new file permission
+ * bits based on the ACL.  In addition, if the ACL is equivalent to the new
+ * file mode, set *acl to NULL to indicate that no ACL should be set.
+ *
+ * As with chmod, clear the setgit bit if the caller is not in the owning group
+ * or capable of CAP_FSETID (see inode_change_ok).
+ *
+ * Called from set_acl inode operations.
+ */
+int posix_acl_update_mode(struct inode *inode, umode_t *mode_p,
+                         struct posix_acl **acl)
+{
+       umode_t mode = inode->i_mode;
+       int error;
+
+       error = posix_acl_equiv_mode(*acl, &mode);
+       if (error < 0)
+               return error;
+       if (error == 0)
+               *acl = NULL;
+       if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
+               mode &= ~S_ISGID;
+       *mode_p = mode;
+       return 0;
+}
+EXPORT_SYMBOL(posix_acl_update_mode);
+
 /*
  * Modify the ACL for the chmod syscall.
  */

diff --git a/fs/reiserfs/xattr_acl.c b/fs/reiserfs/xattr_acl.c
index 6da0396..1d4f4c7 100644 (file)
--- a/fs/reiserfs/xattr_acl.c
+++ b/fs/reiserfs/xattr_acl.c
@@ -272,13 +272,9 @@ reiserfs_set_acl(struct reiserfs_transaction_handle *th, struct inode *inode,
        case ACL_TYPE_ACCESS:
                name = POSIX_ACL_XATTR_ACCESS;
                if (acl) {
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (error)
                                return error;
-                       else {
-                               if (error == 0)
-                                       acl = NULL;
-                       }
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
index f224313..ebed5a8 100644 (file)
--- a/fs/xfs/xfs_acl.c
+++ b/fs/xfs/xfs_acl.c
@@ -384,17 +384,14 @@ xfs_xattr_acl_set(struct dentry *dentry, const char *name,
                goto out_release;
 
        if (type == ACL_TYPE_ACCESS) {
-               umode_t mode = inode->i_mode;
-               error = posix_acl_equiv_mode(acl, &mode);
-
-               if (error <= 0) {
-                       posix_acl_release(acl);
-                       acl = NULL;
-
-                       if (error < 0)
-                               return error;
-               }
+               struct posix_acl *saved_acl = acl;
+               umode_t mode;
 
+               error = posix_acl_update_mode(inode, &mode, &acl);
+               if (error || acl == NULL)
+                       posix_acl_release(saved_acl);
+               if (error)
+                       return error;
                error = xfs_set_mode(dentry, inode, mode);
                if (error)
                        goto out_release;

diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index b768110..da43286 100644 (file)
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -83,6 +83,7 @@ extern struct posix_acl *posix_acl_from_mode(umode_t, gfp_t);
 extern int posix_acl_equiv_mode(const struct posix_acl *, umode_t *);
 extern int posix_acl_create(struct posix_acl **, gfp_t, umode_t *);
 extern int posix_acl_chmod(struct posix_acl **, gfp_t, umode_t);
+extern int posix_acl_update_mode(struct inode *, umode_t *, struct posix_acl **);
 
 extern struct posix_acl *get_posix_acl(struct inode *, int);
 extern int set_posix_acl(struct inode *, int, struct posix_acl *);