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Subject[34-longterm 135/209] filter: make sure filters dont read uninitialized memory
Date
From: David S. Miller <davem@davemloft.net>

=====================================================================
| This is a commit scheduled for the next v2.6.34 longterm release. |
| If you see a problem with using this for longterm, please comment.|
=====================================================================

commit 57fe93b374a6b8711995c2d466c502af9f3a08bb upstream

There is a possibility malicious users can get limited information about
uninitialized stack mem array. Even if sk_run_filter() result is bound
to packet length (0 .. 65535), we could imagine this can be used by
hostile user.

Initializing mem[] array, like Dan Rosenberg suggested in his patch is
expensive since most filters dont even use this array.

Its hard to make the filter validation in sk_chk_filter(), because of
the jumps. This might be done later.

In this patch, I use a bitmap (a single long var) so that only filters
using mem[] loads/stores pay the price of added security checks.

For other filters, additional cost is a single instruction.

[ Since we access fentry->k a lot now, cache it in a local variable
and mark filter entry pointer as const. -DaveM ]

Reported-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
net/core/filter.c | 64 +++++++++++++++++++++++++++++------------------------
1 files changed, 35 insertions(+), 29 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index ff943be..3462e9d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -112,39 +112,41 @@ EXPORT_SYMBOL(sk_filter);
*/
unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int flen)
{
- struct sock_filter *fentry; /* We walk down these */
void *ptr;
u32 A = 0; /* Accumulator */
u32 X = 0; /* Index Register */
u32 mem[BPF_MEMWORDS]; /* Scratch Memory Store */
+ unsigned long memvalid = 0;
u32 tmp;
int k;
int pc;

+ BUILD_BUG_ON(BPF_MEMWORDS > BITS_PER_LONG);
/*
* Process array of filter instructions.
*/
for (pc = 0; pc < flen; pc++) {
- fentry = &filter[pc];
+ const struct sock_filter *fentry = &filter[pc];
+ u32 f_k = fentry->k;

switch (fentry->code) {
case BPF_ALU|BPF_ADD|BPF_X:
A += X;
continue;
case BPF_ALU|BPF_ADD|BPF_K:
- A += fentry->k;
+ A += f_k;
continue;
case BPF_ALU|BPF_SUB|BPF_X:
A -= X;
continue;
case BPF_ALU|BPF_SUB|BPF_K:
- A -= fentry->k;
+ A -= f_k;
continue;
case BPF_ALU|BPF_MUL|BPF_X:
A *= X;
continue;
case BPF_ALU|BPF_MUL|BPF_K:
- A *= fentry->k;
+ A *= f_k;
continue;
case BPF_ALU|BPF_DIV|BPF_X:
if (X == 0)
@@ -152,49 +154,49 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
A /= X;
continue;
case BPF_ALU|BPF_DIV|BPF_K:
- A /= fentry->k;
+ A /= f_k;
continue;
case BPF_ALU|BPF_AND|BPF_X:
A &= X;
continue;
case BPF_ALU|BPF_AND|BPF_K:
- A &= fentry->k;
+ A &= f_k;
continue;
case BPF_ALU|BPF_OR|BPF_X:
A |= X;
continue;
case BPF_ALU|BPF_OR|BPF_K:
- A |= fentry->k;
+ A |= f_k;
continue;
case BPF_ALU|BPF_LSH|BPF_X:
A <<= X;
continue;
case BPF_ALU|BPF_LSH|BPF_K:
- A <<= fentry->k;
+ A <<= f_k;
continue;
case BPF_ALU|BPF_RSH|BPF_X:
A >>= X;
continue;
case BPF_ALU|BPF_RSH|BPF_K:
- A >>= fentry->k;
+ A >>= f_k;
continue;
case BPF_ALU|BPF_NEG:
A = -A;
continue;
case BPF_JMP|BPF_JA:
- pc += fentry->k;
+ pc += f_k;
continue;
case BPF_JMP|BPF_JGT|BPF_K:
- pc += (A > fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A > f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGE|BPF_K:
- pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A >= f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JEQ|BPF_K:
- pc += (A == fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A == f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JSET|BPF_K:
- pc += (A & fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A & f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_JMP|BPF_JGT|BPF_X:
pc += (A > X) ? fentry->jt : fentry->jf;
@@ -209,7 +211,7 @@ unsigned int sk_run_filter(struct sk_buff *skb, struct sock_filter *filter, int
pc += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_LD|BPF_W|BPF_ABS:
- k = fentry->k;
+ k = f_k;
load_w:
ptr = load_pointer(skb, k, 4, &tmp);
if (ptr != NULL) {
@@ -218,7 +220,7 @@ load_w:
}
break;
case BPF_LD|BPF_H|BPF_ABS:
- k = fentry->k;
+ k = f_k;
load_h:
ptr = load_pointer(skb, k, 2, &tmp);
if (ptr != NULL) {
@@ -227,7 +229,7 @@ load_h:
}
break;
case BPF_LD|BPF_B|BPF_ABS:
- k = fentry->k;
+ k = f_k;
load_b:
ptr = load_pointer(skb, k, 1, &tmp);
if (ptr != NULL) {
@@ -242,32 +244,34 @@ load_b:
X = skb->len;
continue;
case BPF_LD|BPF_W|BPF_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_w;
case BPF_LD|BPF_H|BPF_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_h;
case BPF_LD|BPF_B|BPF_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_b;
case BPF_LDX|BPF_B|BPF_MSH:
- ptr = load_pointer(skb, fentry->k, 1, &tmp);
+ ptr = load_pointer(skb, f_k, 1, &tmp);
if (ptr != NULL) {
X = (*(u8 *)ptr & 0xf) << 2;
continue;
}
return 0;
case BPF_LD|BPF_IMM:
- A = fentry->k;
+ A = f_k;
continue;
case BPF_LDX|BPF_IMM:
- X = fentry->k;
+ X = f_k;
continue;
case BPF_LD|BPF_MEM:
- A = mem[fentry->k];
+ A = (memvalid & (1UL << f_k)) ?
+ mem[f_k] : 0;
continue;
case BPF_LDX|BPF_MEM:
- X = mem[fentry->k];
+ X = (memvalid & (1UL << f_k)) ?
+ mem[f_k] : 0;
continue;
case BPF_MISC|BPF_TAX:
X = A;
@@ -276,14 +280,16 @@ load_b:
A = X;
continue;
case BPF_RET|BPF_K:
- return fentry->k;
+ return f_k;
case BPF_RET|BPF_A:
return A;
case BPF_ST:
- mem[fentry->k] = A;
+ memvalid |= 1UL << f_k;
+ mem[f_k] = A;
continue;
case BPF_STX:
- mem[fentry->k] = X;
+ memvalid |= 1UL << f_k;
+ mem[f_k] = X;
continue;
default:
WARN_ON(1);
--
1.7.4.4


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