Check for immutable/append flag in fallocate path

In the fallocate path the kernel doesn't check for the immutable/append
flag. It's possible to have a race condition in this scenario: an
application open a file in read/write and it does something, meanwhile
root set the immutable flag on the file, the application at that point
can call fallocate with success. In addition, we don't allow to do any
unreserve operation on an append only file but only the reserve one.

Signed-off-by: Marco Stornelli <marco.stornelli@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/open.c b/fs/open.c
index 5a2c6ebc22b5d9a1e355050cb14d3218f7a9d0d3..b47aab39c0572242c607495c37c15928fbf8290c 100644 (file)
--- a/fs/open.c
+++ b/fs/open.c
@@ -233,6 +233,14 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 
        if (!(file->f_mode & FMODE_WRITE))
                return -EBADF;
+
+       /* It's not possible punch hole on append only file */
+       if (mode & FALLOC_FL_PUNCH_HOLE && IS_APPEND(inode))
+               return -EPERM;
+
+       if (IS_IMMUTABLE(inode))
+               return -EPERM;
+
        /*
         * Revalidate the write permissions, in case security policy has
         * changed since the files were opened.