Re: mmap() doesn't like certain value...

DervishD
2002-05-10T23:45:27Z

Hi Denis and Marcelo :)

>> And is corrected just by inverting the two quoted code snips :)
>You are right

I've added a couple of comments and one more test. I don't think
that mmap() should return 'addr' when len=0. Moreover, mmap() cannot
return '0' under *any* circumstance (so says the man page).

I've tested the patch with a little program to test every
possible 'len' value and checking for mmap() returning the correct
value.

This is the patch:

--- begin ---

--- mm/mmap.c.orig 2002-05-10 10:40:51.000000000 +0200
+++ mm/mmap.c 2002-05-10 10:47:54.000000000 +0200
@@ -389,6 +389,11 @@
return 0;
}

+
+/*
+ NOTE: in this function we rely on TASK_SIZE being lower than
+SIZE_MAX-PAGE_SIZE at least. I'm pretty sure that it is.
+*/
unsigned long do_mmap_pgoff(struct file * file, unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags, unsigned long pgoff)
{
@@ -402,12 +407,11 @@
if (file && (!file->f_op || !file->f_op->mmap))
return -ENODEV;

- if ((len = PAGE_ALIGN(len)) == 0)
- return addr;
-
- if (len > TASK_SIZE)
+ if (!len || len > TASK_SIZE)
return -EINVAL;

+ len = PAGE_ALIGN(len); /* This CANNOT be zero */
+
/* offset overflow? */
if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
return -EINVAL;

--- end ---

>> I'll give a try to the inversion, that should work. I have
>> written a small stress program for mmap, so in a few hours the patch
>> will be ready. Must I post it here or send it directly to Marcello?
>Post here and to Marcelo. BTW, is 2.5 affected?

I don't really know, but I'm pretty sure... Anyway I think that
the same patch is valid for both kernels with little or no
modification.

BTW, the patch is not only mine, David Gómez Espinosa
(davidge@viadomus.com) has helped me with this issue too.

Raúl