From 939a9421eb53d3ea83188ae13802779041caefdb Mon Sep 17 00:00:00 2001 From: Amerigo Wang Date: Thu, 20 Aug 2009 19:29:03 -0700 Subject: [PATCH] vfs: allow file truncations when both suid and write permissions set When suid is set and the non-owner user has write permission, any writing into this file should be allowed and suid should be removed after that. However, current kernel only allows writing without truncations, when we do truncations on that file, we get EPERM. This is a bug. Steps to reproduce this bug: % ls -l rootdir/file1 -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 % echo h > rootdir/file1 zsh: operation not permitted: rootdir/file1 % ls -l rootdir/file1 -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 % echo h >> rootdir/file1 % ls -l rootdir/file1 -rwxrwxrwx 1 root root 5 Jun 25 16:34 rootdir/file1 Signed-off-by: WANG Cong Cc: Eric Sandeen Acked-by: Eric Paris Cc: Eugene Teo Cc: Al Viro Cc: OGAWA Hirofumi Cc: Christoph Hellwig Cc: Stephen Smalley Signed-off-by: Andrew Morton Signed-off-by: James Morris --- fs/open.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/fs/open.c b/fs/open.c index dd98e8076024..40d1fa25f5aa 100644 --- a/fs/open.c +++ b/fs/open.c @@ -199,7 +199,7 @@ out: int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs, struct file *filp) { - int err; + int ret; struct iattr newattrs; /* Not pretty: "inode->i_size" shouldn't really be signed. But it is. */ @@ -214,12 +214,14 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs, } /* Remove suid/sgid on truncate too */ - newattrs.ia_valid |= should_remove_suid(dentry); + ret = should_remove_suid(dentry); + if (ret) + newattrs.ia_valid |= ret | ATTR_FORCE; mutex_lock(&dentry->d_inode->i_mutex); - err = notify_change(dentry, &newattrs); + ret = notify_change(dentry, &newattrs); mutex_unlock(&dentry->d_inode->i_mutex); - return err; + return ret; } static long do_sys_truncate(const char __user *pathname, loff_t length) -- 2.20.1