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authorEric Dumazet <edumazet@google.com>2014-01-15 06:50:07 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-02-06 11:08:16 -0800
commitcd7361dc9fa60c35d011d674d48eababcc3eb767 (patch)
tree51c5b5cdfabf829671688e9df26623fa64feb5ea /net
parent8c035b62e21a2d26c1a5181ee0d27a76c8996be8 (diff)
downloadlinaro-lsk-cd7361dc9fa60c35d011d674d48eababcc3eb767.tar.gz
bpf: do not use reciprocal divide
[ Upstream commit aee636c4809fa54848ff07a899b326eb1f9987a2 ] At first Jakub Zawadzki noticed that some divisions by reciprocal_divide were not correct. (off by one in some cases) http://www.wireshark.org/~darkjames/reciprocal-buggy.c He could also show this with BPF: http://www.wireshark.org/~darkjames/set-and-dump-filter-k-bug.c The reciprocal divide in linux kernel is not generic enough, lets remove its use in BPF, as it is not worth the pain with current cpus. Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Jakub Zawadzki <darkjames-ws@darkjames.pl> Cc: Mircea Gherzan <mgherzan@gmail.com> Cc: Daniel Borkmann <dxchgb@gmail.com> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Cc: Matt Evans <matt@ozlabs.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: David S. Miller <davem@davemloft.net> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r--net/core/filter.c30
1 files changed, 2 insertions, 28 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 6438f29ff26..52f01229ee0 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -36,7 +36,6 @@
#include <asm/uaccess.h>
#include <asm/unaligned.h>
#include <linux/filter.h>
-#include <linux/reciprocal_div.h>
#include <linux/ratelimit.h>
#include <linux/seccomp.h>
#include <linux/if_vlan.h>
@@ -166,7 +165,7 @@ unsigned int sk_run_filter(const struct sk_buff *skb,
A /= X;
continue;
case BPF_S_ALU_DIV_K:
- A = reciprocal_divide(A, K);
+ A /= K;
continue;
case BPF_S_ALU_MOD_X:
if (X == 0)
@@ -553,11 +552,6 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
/* Some instructions need special checks */
switch (code) {
case BPF_S_ALU_DIV_K:
- /* check for division by zero */
- if (ftest->k == 0)
- return -EINVAL;
- ftest->k = reciprocal_value(ftest->k);
- break;
case BPF_S_ALU_MOD_K:
/* check for division by zero */
if (ftest->k == 0)
@@ -853,27 +847,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
to->code = decodes[code];
to->jt = filt->jt;
to->jf = filt->jf;
-
- if (code == BPF_S_ALU_DIV_K) {
- /*
- * When loaded this rule user gave us X, which was
- * translated into R = r(X). Now we calculate the
- * RR = r(R) and report it back. If next time this
- * value is loaded and RRR = r(RR) is calculated
- * then the R == RRR will be true.
- *
- * One exception. X == 1 translates into R == 0 and
- * we can't calculate RR out of it with r().
- */
-
- if (filt->k == 0)
- to->k = 1;
- else
- to->k = reciprocal_value(filt->k);
-
- BUG_ON(reciprocal_value(to->k) != filt->k);
- } else
- to->k = filt->k;
+ to->k = filt->k;
}
int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf, unsigned int len)