flen is indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
net/core/filter.c:1101 bpf_check_classic() warn: potential spectre issue
'filter' [w]
Fix this by sanitizing flen before using it to index filter at line 1101:
switch (filter[flen - 1].code) {
and through pc at line 1040:
const struct sock_filter *ftest = &filter[pc];
Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].
[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2
Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
---
net/core/filter.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index 447dd1bad31f..8ec4337256ed 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -73,6 +73,7 @@
#include <linux/seg6_local.h>
#include <net/seg6.h>
#include <net/seg6_local.h>
+#include <linux/nospec.h>
/**
* sk_filter_trim_cap - run a packet through a socket filter
@@ -1035,6 +1036,7 @@ static int bpf_check_classic(const struct sock_filter
*filter,
bool anc_found;
int pc;
+ flen = array_index_nospec(flen, BPF_MAXINSNS + 1);
/* Check the filter code now */
for (pc = 0; pc < flen; pc++) {
const struct sock_filter *ftest = &filter[pc];
--
2.20.1
