netdev - Re: sha512: make it work, undo percpu message schedule

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Date:	Fri, 13 Jan 2012 11:57:26 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	linux-crypto@...r.kernel.org, netdev@...r.kernel.org,
	ken@...elabs.ch, Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: sha512: make it work, undo percpu message schedule

Le vendredi 13 janvier 2012 à 11:41 +0100, Eric Dumazet a écrit :

> And a plain kmalloc() is enough, since we fully initialize the array a
> bit later.
> 
> 	for (i = 0; i < 16; i++)
> 		LOAD_OP(i, W, input);
> 	for (i = 16; i < 80; i++) {
> 		BLEND_OP(i, W);
> 	}


Here is an official patch ;)

[PATCH v3] crypto: sha512 - Fix msg_schedule race

The percpu msg_schedule setup was unsafe as a user in a process
context can be interrupted by a softirq user which would then
scribble over the exact same work area.

Bug reported by Alexey Dobriyan, and diagnosed by Steffen Klassert.

Bug added in commit f9e2bca6c22 (crypto: sha512 - Move message schedule
W[80] to static percpu area)
    
Try a dynamic memory allocation, and fallback using a single static
area, guarded by a spinlock.

This removes use of percpu memory.

Reported-by: Alexey Dobriyan <adobriyan@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Herbert Xu <herbert@...dor.apana.org.au>
CC: Adrian-Ken Rueegsegger <ken@...elabs.ch>
CC: Steffen Klassert <steffen.klassert@...unet.com>
---
 crypto/sha512_generic.c |   18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/crypto/sha512_generic.c b/crypto/sha512_generic.c
index 9ed9f60..b52ef9b 100644
--- a/crypto/sha512_generic.c
+++ b/crypto/sha512_generic.c
@@ -18,10 +18,8 @@
 #include <linux/crypto.h>
 #include <linux/types.h>
 #include <crypto/sha.h>
-#include <linux/percpu.h>
 #include <asm/byteorder.h>
 
-static DEFINE_PER_CPU(u64[80], msg_schedule);
 
 static inline u64 Ch(u64 x, u64 y, u64 z)
 {
@@ -87,10 +85,15 @@ static void
 sha512_transform(u64 *state, const u8 *input)
 {
 	u64 a, b, c, d, e, f, g, h, t1, t2;
-
+	static u64 msg_schedule[80];
+	static DEFINE_SPINLOCK(msg_schedule_lock);
 	int i;
-	u64 *W = get_cpu_var(msg_schedule);
+	u64 *W = kmalloc(sizeof(msg_schedule), GFP_ATOMIC | __GFP_NOWARN);
 
+	if (!W) {
+		spin_lock_bh(&msg_schedule_lock);
+		W = msg_schedule;
+	}
 	/* load the input */
         for (i = 0; i < 16; i++)
                 LOAD_OP(i, W, input);
@@ -128,8 +131,11 @@ sha512_transform(u64 *state, const u8 *input)
 
 	/* erase our data */
 	a = b = c = d = e = f = g = h = t1 = t2 = 0;
-	memset(W, 0, sizeof(__get_cpu_var(msg_schedule)));
-	put_cpu_var(msg_schedule);
+	memset(W, 0, sizeof(msg_schedule));
+	if (W == msg_schedule)
+		spin_unlock_bh(&msg_schedule_lock);
+	else
+		kfree(W);
 }
 
 static int


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