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[PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page()

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  [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page() Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-12 00:10 +0100
    Re: [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page() David Howells <dhowells@redhat.com> - 2015-11-12 11:20 +0100
      Re: [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page() Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-12 11:30 +0100
        Re: [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page() David Howells <dhowells@redhat.com> - 2015-11-12 11:50 +0100
          Re: [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page() Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-12 11:50 +0100

#1267528 — [PATCH] FS-Cache: Add missing initialization of ret in cachefiles_write_page()

fs/cachefiles/rdwr.c: In function ‘cachefiles_write_page’:
fs/cachefiles/rdwr.c:882: warning: ‘ret’ may be used uninitialized in
this function

If the jump to label "error" is taken, "ret" will indeed be
uninitialized, and random stack data may be printed by the debug code.

Fixes: 102f4d900c9c8f5e ("FS-Cache: Handle a write to the page immediately beyond the EOF marker")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
 fs/cachefiles/rdwr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 7a6b02f727874352..bdd28fe9a7f7195b 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -879,7 +879,7 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 	loff_t pos, eof;
 	size_t len;
 	void *data;
-	int ret;
+	int ret = 0;
 
 	ASSERT(op != NULL);
 	ASSERT(page != NULL);
-- 
1.9.1

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#1267786

Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> -	int ret;
> +	int ret = 0;

This isn't quite the right solution.  The uninitialised error path needs to
set -ENOBUFS.  Unfortunately, my compiler doesn't show a warning:-/

David
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#1267792

Hi David,

On Thu, Nov 12, 2015 at 11:15 AM, David Howells <dhowells@redhat.com> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
>> -     int ret;
>> +     int ret = 0;
>
> This isn't quite the right solution.  The uninitialised error path needs to
> set -ENOBUFS.

That's what your commit 102f4d900c9c8f5e ("FS-Cache: Handle a write to the
page immediately beyond the EOF marker") does, and is also in its commit
description:

    Whilst we're at it, change the triggered assertion in CacheFiles to just
    return -ENOBUFS instead.

"ret" is used only to print the original error in a debug message.

> Unfortunately, my compiler doesn't show a warning:-/

Need old gcc (4.1.2 ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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#1267810

Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> > This isn't quite the right solution.  The uninitialised error path needs to
> > set -ENOBUFS.
> 
> That's what your commit 102f4d900c9c8f5e ("FS-Cache: Handle a write to the
> page immediately beyond the EOF marker") does, and is also in its commit
> description:
> 
>     Whilst we're at it, change the triggered assertion in CacheFiles to just
>     return -ENOBUFS instead.
> 
> "ret" is used only to print the original error in a debug message.

I'll adjust your patch to set the default value in ret to be -ENOBUFS instead
of 0.

> > Unfortunately, my compiler doesn't show a warning:-/
> 
> Need old gcc (4.1.2 ;-)

Quite possibly - gcc-5.1 does seem to be a bit lacking in detection of such
things.

David
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#1267815

On Thu, Nov 12, 2015 at 11:42 AM, David Howells <dhowells@redhat.com> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
>> > This isn't quite the right solution.  The uninitialised error path needs to
>> > set -ENOBUFS.
>>
>> That's what your commit 102f4d900c9c8f5e ("FS-Cache: Handle a write to the
>> page immediately beyond the EOF marker") does, and is also in its commit
>> description:
>>
>>     Whilst we're at it, change the triggered assertion in CacheFiles to just
>>     return -ENOBUFS instead.
>>
>> "ret" is used only to print the original error in a debug message.
>
> I'll adjust your patch to set the default value in ret to be -ENOBUFS instead
> of 0.

OK. Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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