[270/289] filter: make sure filters dont read uninitialized memory

Greg KH
2010-12-08T01:08:45Z

From: David S. Miller <davem@davemloft.net>

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: Greg Kroah-Hartman <gregkh@suse.de>

---
net/core/filter.c | 64 +++++++++++++++++++++++++++++-------------------------
1 file changed, 35 insertions(+), 29 deletions(-)

--- 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_S_ALU_ADD_X:
A += X;
continue;
case BPF_S_ALU_ADD_K:
- A += fentry->k;
+ A += f_k;
continue;
case BPF_S_ALU_SUB_X:
A -= X;
continue;
case BPF_S_ALU_SUB_K:
- A -= fentry->k;
+ A -= f_k;
continue;
case BPF_S_ALU_MUL_X:
A *= X;
continue;
case BPF_S_ALU_MUL_K:
- A *= fentry->k;
+ A *= f_k;
continue;
case BPF_S_ALU_DIV_X:
if (X == 0)
@@ -152,49 +154,49 @@ unsigned int sk_run_filter(struct sk_buf
A /= X;
continue;
case BPF_S_ALU_DIV_K:
- A /= fentry->k;
+ A /= f_k;
continue;
case BPF_S_ALU_AND_X:
A &= X;
continue;
case BPF_S_ALU_AND_K:
- A &= fentry->k;
+ A &= f_k;
continue;
case BPF_S_ALU_OR_X:
A |= X;
continue;
case BPF_S_ALU_OR_K:
- A |= fentry->k;
+ A |= f_k;
continue;
case BPF_S_ALU_LSH_X:
A <<= X;
continue;
case BPF_S_ALU_LSH_K:
- A <<= fentry->k;
+ A <<= f_k;
continue;
case BPF_S_ALU_RSH_X:
A >>= X;
continue;
case BPF_S_ALU_RSH_K:
- A >>= fentry->k;
+ A >>= f_k;
continue;
case BPF_S_ALU_NEG:
A = -A;
continue;
case BPF_S_JMP_JA:
- pc += fentry->k;
+ pc += f_k;
continue;
case BPF_S_JMP_JGT_K:
- pc += (A > fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A > f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGE_K:
- pc += (A >= fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A >= f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JEQ_K:
- pc += (A == fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A == f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JSET_K:
- pc += (A & fentry->k) ? fentry->jt : fentry->jf;
+ pc += (A & f_k) ? fentry->jt : fentry->jf;
continue;
case BPF_S_JMP_JGT_X:
pc += (A > X) ? fentry->jt : fentry->jf;
@@ -209,7 +211,7 @@ unsigned int sk_run_filter(struct sk_buf
pc += (A & X) ? fentry->jt : fentry->jf;
continue;
case BPF_S_LD_W_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_S_LD_H_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_S_LD_B_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_S_LD_W_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_w;
case BPF_S_LD_H_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_h;
case BPF_S_LD_B_IND:
- k = X + fentry->k;
+ k = X + f_k;
goto load_b;
case BPF_S_LDX_B_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_S_LD_IMM:
- A = fentry->k;
+ A = f_k;
continue;
case BPF_S_LDX_IMM:
- X = fentry->k;
+ X = f_k;
continue;
case BPF_S_LD_MEM:
- A = mem[fentry->k];
+ A = (memvalid & (1UL << f_k)) ?
+ mem[f_k] : 0;
continue;
case BPF_S_LDX_MEM:
- X = mem[fentry->k];
+ X = (memvalid & (1UL << f_k)) ?
+ mem[f_k] : 0;
continue;
case BPF_S_MISC_TAX:
X = A;
@@ -276,14 +280,16 @@ load_b:
A = X;
continue;
case BPF_S_RET_K:
- return fentry->k;
+ return f_k;
case BPF_S_RET_A:
return A;
case BPF_S_ST:
- mem[fentry->k] = A;
+ memvalid |= 1UL << f_k;
+ mem[f_k] = A;
continue;
case BPF_S_STX:
- mem[fentry->k] = X;
+ memvalid |= 1UL << f_k;
+ mem[f_k] = X;
continue;
default:
WARN_ON(1);