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authorAmerigo Wang <amwang@redhat.com>2009-08-20 19:29:03 -0700
committerJames Morris <jmorris@namei.org>2009-08-21 14:25:48 +1000
commit939a9421eb53d3ea83188ae13802779041caefdb (patch)
treee782e64e6e3e545a4b7c8ab108b2fcf8d01aa952
parentbc6a6008e5e3c7a30191a7f19ab19e85b14b1705 (diff)
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 <amwang@redhat.com> Cc: Eric Sandeen <esandeen@redhat.com> Acked-by: Eric Paris <eparis@redhat.com> Cc: Eugene Teo <eteo@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Cc: Christoph Hellwig <hch@lst.de> Cc: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: James Morris <jmorris@namei.org>
-rw-r--r--fs/open.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/fs/open.c b/fs/open.c
index dd98e807602..40d1fa25f5a 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)