[patch 2.6.13-rc6] Fix kmem read on 32-bit archs

From: Chuck Ebbert (76306.1226_at_compuserve.com)
Date: 08/14/05

  • Next message: Andi Kleen: "Re: [patch 2.6.13-rc6] Fix kmem read on 32-bit archs" 
    Date:	Sun, 14 Aug 2005 12:12:52 -0400
To: linux-kernel <linux-kernel@vger.kernel.org>

      The first thing drivers/char/mem.c:read_kmem does is convert the
    loff_t it gets as the offset for reading into an unsigned int. This
    patch makes the kmem driver's llseek operator do that up-front, so
    that fs/read_write.c:rw_verify_area doesn't return -EINVAL when
    we try to read from higher addresses.

      It's ugly but so is the existing code. And it won't fix 64-bit
    archs AFAICT. Tested on 2.6.11, patch offsets fixed up for 2.6.13-rc6.

    Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>

    Index: 2.6.13-rc6/drivers/char/mem.c
    ===================================================================
    --- 2.6.13-rc6.orig/drivers/char/mem.c 2005-08-14 11:49:11.000000000 -0400
    +++ 2.6.13-rc6/drivers/char/mem.c 2005-08-14 11:51:15.000000000 -0400
    @@ -747,6 +747,29 @@
             return ret;
     }
     
    +static loff_t kmem_lseek(struct file * file, loff_t offset, int orig)
    +{
    + loff_t ret = -EINVAL;
    +
    + if (orig == 2) /* sys_seek/llseek has checked orig = {012} */
    + goto out;
    +
    + down(&file->f_dentry->d_inode->i_sem);
    + switch (orig) {
    + case 0:
    + file->f_pos = offset;
    + break;
    + case 1:
    + file->f_pos += offset;
    + }
    + ret = file->f_pos;
    + file->f_pos = (loff_t)(unsigned long)file->f_pos;
    + force_successful_syscall_return();
    + up(&file->f_dentry->d_inode->i_sem);
    +out:
    + return ret;
    +}
    +
     static int open_port(struct inode * inode, struct file * filp)
     {
             return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
    @@ -769,7 +792,7 @@
     };
     
     static struct file_operations kmem_fops = {
    - .llseek = memory_lseek,
    + .llseek = kmem_lseek,
             .read = read_kmem,
             .write = write_kmem,
             .mmap = mmap_kmem,
    __
    Chuck
    -
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