[PATCH] Prevent creation of files larger than RLIMIT_FSIZE using fallocate

[Nikanth Karthikesan <knikanth@suse.de>]

Prevent creation of files larger than RLIMIT_FSIZE using fallocate.

Currently using posix_fallocate one can bypass an RLIMIT_FSIZE limit
and create a file larger than the limit. Add a check for new size in
the fallocate system call.

File-systems supporting fallocate such as ext4 are affected by this
bug. 

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Reported-by: Eelis - <opensuse.org@contacts.eelis.net>

---

diff --git a/fs/open.c b/fs/open.c
index 74e5cd9..95ce069 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -412,10 +412,14 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (!S_ISREG(inode->i_mode) && !S_ISDIR(inode->i_mode))
 		return -ENODEV;
 
-	/* Check for wrap through zero too */
-	if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
+	/* Check for wrap through zero */
+	if (offset+len < 0)
 		return -EFBIG;
 
+	ret = inode_newsize_ok(inode, (offset + len));
+	if (ret)
+		return ret;
+
 	if (!inode->i_op->fallocate)
 		return -EOPNOTSUPP;