On 3/27/2018 6:05 PM, Daniel Borkmann wrote:
On 03/27/2018 10:41 AM, Prashant Bhole wrote:
On 3/27/2018 12:15 PM, John Fastabend wrote:
On 03/25/2018 11:54 PM, Prashant Bhole wrote:
When CONFIG_DEBUG_SG is set, sg->sg_magic is initialized to SG_MAGIC,
when sg table is initialized using sg_init_table(). Magic is checked
while navigating the scatterlist. We hit BUG_ON when magic check is
failed.
Fixed following things:
- Initialization of sg table in bpf_tcp_sendpage() was missing,
initialized it using sg_init_table()
- bpf_tcp_sendmsg() initializes sg table using sg_init_table() before
entering the loop, but further consumed sg entries are initialized
using memset. Fixed it by replacing memset with sg_init_table() in
function bpf_tcp_push()
Signed-off-by: Prashant Bhole <bhole_prashant...@lab.ntt.co.jp>
---
kernel/bpf/sockmap.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 69c5bccabd22..8a848a99d768 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -312,7 +312,7 @@ static int bpf_tcp_push(struct sock *sk, int apply_bytes,
md->sg_start++;
if (md->sg_start == MAX_SKB_FRAGS)
md->sg_start = 0;
- memset(sg, 0, sizeof(*sg));
+ sg_init_table(sg, 1);
Looks OK here.
if (md->sg_start == md->sg_end)
break;
@@ -763,10 +763,14 @@ static int bpf_tcp_sendpage(struct sock *sk, struct page
*page,
lock_sock(sk);
- if (psock->cork_bytes)
+ if (psock->cork_bytes) {
m = psock->cork;
- else
+ sg = &m->sg_data[m->sg_end];
+ } else {
m = &md;
+ sg = m->sg_data;
+ sg_init_table(sg, MAX_SKB_FRAGS);
sg_init_table() does an unnecessary memset() though. We
probably either want a new scatterlist API or just open
code this,
#ifdef CONFIG_DEBUG_SG
{
unsigned int i;
for (i = 0; i < nents; i++)
sgl[i].sg_magic = SG_MAGIC;
}
Similar sg_init_table() is present in bpf_tcp_sendmsg().
I agree that it causes unnecessary memset, but I don't agree with open coded
fix.
But then lets fix is properly and add a static inline helper to the
include/linux/scatterlist.h header like ...
static inline void sg_init_debug_marker(struct scatterlist *sgl,
unsigned int nents)
{
#ifdef CONFIG_DEBUG_SG
unsigned int i;
for (i = 0; i < nents; i++)
sgl[i].sg_magic = SG_MAGIC;
#endif
}
... and reuse it in all the places that would otherwise open-code this,
as well as sg_init_table():
void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
memset(sgl, 0, sizeof(*sgl) * nents);
sg_init_debug_marker(sgl, nents);
sg_mark_end(&sgl[nents - 1]);
}
This would be a lot cleaner than having this duplicated in various places.
Daniel, This is a good suggestion. Is it ok if I submit both changes in
a patch series? How scatterlist related changes will be picked up by
other subsystems?
-Prashant
