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filter: make sure filters dont read uninitialized memory

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commit 57fe93b374 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>
[Backported by dann frazier <dannf@debian.org>]
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
David S. Miller
2010-11-10 10:38:24 -08:00
committed by Greg Kroah-Hartman
parent 12d83a21da
commit f37c091b7f
1 changed files with 35 additions and 29 deletions
Download Patch File Download Diff File Expand all files Collapse all files

64
net/core/filter.c
View File

@@ -111,39 +111,41 @@ 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)
@@ -151,49 +153,49 @@ 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;
@@ -208,7 +210,7 @@ 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) {
@@ -217,7 +219,7 @@ 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) {
@@ -226,7 +228,7 @@ 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) {
@@ -241,32 +243,34 @@ 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;
@@ -275,14 +279,16 @@ 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);