* Re: 2.5.55-rmk1: user space lossage
[not found] <000001c2c287$ffa8eef0$800b040f@bergamot>
@ 2003-01-23 9:48 ` David Woodhouse
2003-01-23 9:56 ` Andrew Morton
2003-01-23 10:01 ` David Woodhouse
0 siblings, 2 replies; 5+ messages in thread
From: David Woodhouse @ 2003-01-23 9:48 UTC (permalink / raw)
To: Christopher Hoover
Cc: 'Frank Becker', linux-arm-kernel, 'linux-mtd',
akpm, linux-kernel
< Snip long thread about init segfaulting immediately at boot on 2.5.55 >
ch@murgatroid.com said:
> I just dropped jffs2 from 2.5.52 into 2.5.55 and it works, too.
ch@murgatroid.com said:
> Aha! This is the problem:
> - .mmap = generic_file_mmap,
> + .mmap = generic_file_readonly_mmap,
> If you reverese this change, 2.5.55-rmk1 behaves.
Er, yes. generic_file_readonly_mmap() silently removed the VM_MAYWRITE bit
from vma->vm_flags when init made a _PRIVATE_ writable mapping, apparently
on the basis that we have no writepage().
Then we return success anyway.
Then init segfaults when it touches something in that mapping.
/me blames akpm. :)
--
dwmw2
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage
2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse
@ 2003-01-23 9:56 ` Andrew Morton
2003-01-23 10:01 ` David Woodhouse
1 sibling, 0 replies; 5+ messages in thread
From: Andrew Morton @ 2003-01-23 9:56 UTC (permalink / raw)
To: David Woodhouse; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel
David Woodhouse <dwmw2@infradead.org> wrote:
>
> /me blames akpm. :)
Linus did it!
diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c
--- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41.000000000 -0800
+++ 25-akpm/mm/filemap.c 2003-01-23 01:55:45.000000000 -0800
@@ -1312,7 +1312,6 @@ int generic_file_readonly_mmap(struct fi
{
if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
return -EINVAL;
- vma->vm_flags &= ~VM_MAYWRITE;
return generic_file_mmap(file, vma);
}
#else
_
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage
2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse
2003-01-23 9:56 ` Andrew Morton
@ 2003-01-23 10:01 ` David Woodhouse
2003-01-23 10:06 ` Andrew Morton
1 sibling, 1 reply; 5+ messages in thread
From: David Woodhouse @ 2003-01-23 10:01 UTC (permalink / raw)
To: Andrew Morton; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel
akpm@digeo.com said:
> Linus did it!
> diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c
> --- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41 -0800
> +++ 25-akpm/mm/filemap.c 2003-01-23 01:55:45 -0800
> @@ -1312,7 +1312,6 @@ int generic_file_readonly_mmap(struct fi
> {
> if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
> return -EINVAL;
> - vma->vm_flags &= ~VM_MAYWRITE;
> return generic_file_mmap(file, vma);
> }
> #else
- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
+- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
++ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
...?
--
dwmw2
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage
2003-01-23 10:01 ` David Woodhouse
@ 2003-01-23 10:06 ` Andrew Morton
2003-01-23 17:57 ` Hugh Dickins
0 siblings, 1 reply; 5+ messages in thread
From: Andrew Morton @ 2003-01-23 10:06 UTC (permalink / raw)
To: David Woodhouse; +Cc: ch, fbecker, linux-arm-kernel, linux-mtd, linux-kernel
David Woodhouse <dwmw2@infradead.org> wrote:
>
>
>
> - if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
> +- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
> ++ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
Yup.
We cannot clear VM_MAYWRITE in there - it turns writeable MAP_PRIVATE
mappings into readonly ones.
So change it back to the 2.4 form - disallow a writeable MAP_SHARED mapping
against filesystems which do no implement ->writepage().
filemap.c | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff -puN mm/filemap.c~generic_file_readonly_mmap-fix mm/filemap.c
--- 25/mm/filemap.c~generic_file_readonly_mmap-fix 2003-01-23 01:55:41.000000000 -0800
+++ 25-akpm/mm/filemap.c 2003-01-23 02:04:05.000000000 -0800
@@ -1308,11 +1308,13 @@ int generic_file_mmap(struct file * file
return 0;
}
+/*
+ * This is for filesystems which do not implement ->writepage.
+ */
int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
{
- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
+ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
return -EINVAL;
- vma->vm_flags &= ~VM_MAYWRITE;
return generic_file_mmap(file, vma);
}
#else
_
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: 2.5.55-rmk1: user space lossage
2003-01-23 10:06 ` Andrew Morton
@ 2003-01-23 17:57 ` Hugh Dickins
0 siblings, 0 replies; 5+ messages in thread
From: Hugh Dickins @ 2003-01-23 17:57 UTC (permalink / raw)
To: Andrew Morton; +Cc: David Woodhouse, linux-kernel
On Thu, 23 Jan 2003, Andrew Morton wrote:
>
> We cannot clear VM_MAYWRITE in there - it turns writeable MAP_PRIVATE
> mappings into readonly ones.
>
> So change it back to the 2.4 form - disallow a writeable MAP_SHARED mapping
> against filesystems which do no implement ->writepage().
Sorry for late quibbles, but wouldn't patch below be better? Linus
did intend that change to the occasionally criticized 2.4 behaviour,
this preserves that change while avoiding the bug which hit David.
You may notice I've sneaked a ~VM_SHARED in there too. Not because
I can say it's necessary, but the VM_MAYWRITE, VM_SHARED treatment
is already weird, I'd feel safer if we keep to the same combination
as already exists in the !FMODE_WRITE case (see do_mmap_pgoff).
Hugh
--- 2.5.59-mm2/mm/filemap.c Sat Jan 18 10:37:36 2003
+++ linux/mm/filemap.c Thu Jan 23 16:50:34 2003
@@ -1310,9 +1310,11 @@
int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
{
- if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE))
- return -EINVAL;
- vma->vm_flags &= ~VM_MAYWRITE;
+ if (vma->vm_flags & VM_SHARED) {
+ if (vma->vm_flags & VM_WRITE)
+ return -EINVAL;
+ vma->vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
+ }
return generic_file_mmap(file, vma);
}
#else
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2003-01-23 17:46 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
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2003-01-23 9:48 ` 2.5.55-rmk1: user space lossage David Woodhouse
2003-01-23 9:56 ` Andrew Morton
2003-01-23 10:01 ` David Woodhouse
2003-01-23 10:06 ` Andrew Morton
2003-01-23 17:57 ` Hugh Dickins
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