Merge branch 'bpf-sockmap-sg-api-fixes'

Prashant Bhole says:

====================
These patches fix sg api usage in sockmap. Previously sockmap didn't
use sg_init_table(), which caused hitting BUG_ON in sg api, when
CONFIG_DEBUG_SG is enabled

v1: added sg_init_table() calls wherever needed.

v2:
- Patch1 adds new helper function in sg api. sg_init_marker()
- Patch2 sg_init_marker() and sg_init_table() in appropriate places

Backgroud:
While reviewing v1, John Fastabend raised a valid point about
unnecessary memset in sg_init_table() because sockmap uses sg table
which embedded in a struct. As enclosing struct is zeroed out, there
is unnecessary memset in sg_init_table.

So Daniel Borkmann suggested to define another static inline function
in scatterlist.h which only initializes sg_magic. Also this function
will be called from sg_init_table. From this suggestion I defined a
function sg_init_marker() which sets sg_magic and calls sg_mark_end()
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

3 files changed, 27 insertions, 13 deletions

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 22b2131bcdcd..aa5d4eb725f5 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -248,6 +248,24 @@ static inline void *sg_virt(struct scatterlist *sg)
         return page_address(sg_page(sg)) + sg->offset;
 }
 
+/**
+ * sg_init_marker - Initialize markers in sg table
+ * @sgl:           The SG table
+ * @nents:         Number of entries in table
+ *
+ **/
+static inline void sg_init_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
+        sg_mark_end(&sgl[nents - 1]);
+}
+
 int sg_nents(struct scatterlist *sg);
 int sg_nents_for_len(struct scatterlist *sg, u64 len);
 struct scatterlist *sg_next(struct scatterlist *);
diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 9192fdbcbccc..d2bda5aa25d7 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -341,7 +341,7 @@ retry:
                         md->sg_start++;
                         if (md->sg_start == MAX_SKB_FRAGS)
                                 md->sg_start = 0;
-                        memset(sg, 0, sizeof(*sg));
+                        sg_init_table(sg, 1);
 
                         if (md->sg_start == md->sg_end)
                                 break;
@@ -843,7 +843,7 @@ static int bpf_tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
         }
 
         sg = md.sg_data;
-        sg_init_table(sg, MAX_SKB_FRAGS);
+        sg_init_marker(sg, MAX_SKB_FRAGS);
         rcu_read_unlock();
 
         lock_sock(sk);
@@ -950,10 +950,14 @@ 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_marker(sg, MAX_SKB_FRAGS);
+        }
 
         /* Catch case where ring is full and sendpage is stalled. */
         if (unlikely(m->sg_end == m->sg_start &&
@@ -961,7 +965,6 @@ static int bpf_tcp_sendpage(struct sock *sk, struct page *page,
                 goto out_err;
 
         psock->sg_size += size;
-        sg = &m->sg_data[m->sg_end];
         sg_set_page(sg, page, size, offset);
         get_page(page);
         m->sg_copy[m->sg_end] = true;
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 53728d391d3a..06dad7a072fd 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -132,14 +132,7 @@ EXPORT_SYMBOL(sg_last);
 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
 {
         memset(sgl, 0, sizeof(*sgl) * nents);
-#ifdef CONFIG_DEBUG_SG
-        {
-                unsigned int i;
-                for (i = 0; i < nents; i++)
-                        sgl[i].sg_magic = SG_MAGIC;
-        }
-#endif
-        sg_mark_end(&sgl[nents - 1]);
+        sg_init_marker(sgl, nents);
 }
 EXPORT_SYMBOL(sg_init_table);