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[PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

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  [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i Colin King <colin.king@canonical.com> - 2016-09-17 12:30 +0200
    Re: [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when  decrementing index i Borislav Petkov <bp@suse.de> - 2016-09-19 20:00 +0200

#1485517 — [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

From: Colin Ian King <colin.king@canonical.com>

Change predecrement compare to post decrement compare to avoid an
unsigned integer wrap-around comparisomn when decrementing in the while
loop.

For example, if the debugfs_create_file fails when i is zero, the
current situation will predecrement i in the while loop, wrapping i
to the maximum signed integer and cause multiple out of bounds reads
on dfs_fls[i].d as the loop interates to zero.

Also, as Borislav Petkov suggested, return -ENODEV rather than -ENOMEM
on the error condition.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 arch/x86/ras/mce_amd_inj.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
index cd318d9..20b227f 100644
--- a/arch/x86/ras/mce_amd_inj.c
+++ b/arch/x86/ras/mce_amd_inj.c
@@ -464,13 +464,13 @@ static int __init init_mce_inject(void)
 	return 0;
 
 err_dfs_add:
-	while (--i >= 0)
+	while (i-- > 0)
 		debugfs_remove(dfs_fls[i].d);
 
 	debugfs_remove(dfs_inj);
 	dfs_inj = NULL;
 
-	return -ENOMEM;
+	return -ENODEV;
 }
 
 static void __exit exit_mce_inject(void)
-- 
2.9.3

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#1486731 — Re: [PATCH][V3] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

On Sat, Sep 17, 2016 at 11:17:50AM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> Change predecrement compare to post decrement compare to avoid an
> unsigned integer wrap-around comparisomn when decrementing in the while
> loop.
> 
> For example, if the debugfs_create_file fails when i is zero, the
> current situation will predecrement i in the while loop, wrapping i
> to the maximum signed integer and cause multiple out of bounds reads
> on dfs_fls[i].d as the loop interates to zero.
> 
> Also, as Borislav Petkov suggested, return -ENODEV rather than -ENOMEM
> on the error condition.
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  arch/x86/ras/mce_amd_inj.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
> index cd318d9..20b227f 100644
> --- a/arch/x86/ras/mce_amd_inj.c
> +++ b/arch/x86/ras/mce_amd_inj.c
> @@ -464,13 +464,13 @@ static int __init init_mce_inject(void)
>  	return 0;
>  
>  err_dfs_add:
> -	while (--i >= 0)
> +	while (i-- > 0)

Even better.

Applied,
thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

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