Re: [PATCH][V2][Fix commit message] x86/RAS/mce_amd_inj: fix signed wrap around when decrementing index i

From: Borislav Petkov
Date: Sat Sep 17 2016 - 03:35:44 EST

(drop peterz from CC).

On Fri, Sep 16, 2016 at 12:22:23PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> Integer index i needs to be a signed int rather than unsigned to avoid
> a wrap-around when decrementing in the while loop. For example, if the

Damn corner cases :-\

> 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 add (int) cast to fix warning that the original fix attempted
> to fix.

Thanks, that's a good catch!

But, can we keep the unsigned-ness of i as it is an index and do this

(Oh, and make it return ENODEV - that ENOMEM is just plain wrong most of
the time).

diff --git a/arch/x86/ras/mce_amd_inj.c b/arch/x86/ras/mce_amd_inj.c
index cd318d93099e..a2dafca467e6 100644
--- a/arch/x86/ras/mce_amd_inj.c
+++ b/arch/x86/ras/mce_amd_inj.c
@@ -457,8 +457,12 @@ static int __init init_mce_inject(void)

- if (!dfs_fls[i].d)
+ if (!dfs_fls[i].d) {
+ if (!i)
+ return -ENODEV;
goto err_dfs_add;
+ }

return 0;
@@ -470,7 +474,7 @@ err_dfs_add:
dfs_inj = NULL;

- return -ENOMEM;
+ return -ENODEV;

static void __exit exit_mce_inject(void)


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