[PATCH 1/2] seq_buf: fix overflow in seq_buf_putmem_hex()

[PATCH 1/2] seq_buf: fix overflow in seq_buf_putmem_hex()

[Yun Zhou]

There's two variables being increased in that loop (i and j), and i
follows the raw data, and j follows what is being written into the buffer.
We should compare 'i' to MAX_MEMHEX_BYTES or compare 'j' to HEX_CHARS.
Otherwise, if 'j' goes bigger than HEX_CHARS, it will overflow the
destination buffer.

This bug exists in the original code (commit 5e3ca0ec76fce 'ftrace:
introduce the "hex" output method'). Although its original design did
not support more than 8 bytes, the only check on length seems to have
mistaken the comparison object, 'len' should compare to 'HEX_CHARS/2'.
    BUG_ON(len >= HEX_CHARS);

Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
---
 lib/seq_buf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index 6aabb609dd87..223fbc3bb958 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -228,8 +228,10 @@ int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
 
 	WARN_ON(s->size == 0);
 
+	BUILD_BUG_ON(MAX_MEMHEX_BYTES * 2 >= HEX_CHARS);
+
 	while (len) {
-		start_len = min(len, HEX_CHARS - 1);
+		start_len = min(len, MAX_MEMHEX_BYTES);
 #ifdef __BIG_ENDIAN
 		for (i = 0, j = 0; i < start_len; i++) {
 #else
-- 
2.26.1

[PATCH 2/2] seq_buf: Make trace_seq_putmem_hex() support data longer than 8

[Yun Zhou]

Since the raw memory 'data' does not go forward, it will dump repeated
data if the data length is more than 8. If we want to dump longer data
blocks, we need to repeatedly call macro SEQ_PUT_HEX_FIELD. I think it
is a bit redundant, and multiple function calls also affect the performance.

This patch is to improve the commit 6d2289f3faa7 ("tracing: Make
trace_seq_putmem_hex() more robust").

Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
---
 lib/seq_buf.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index 223fbc3bb958..562e53c93b7b 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -244,12 +244,14 @@ int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
 			break;
 
 		/* j increments twice per loop */
-		len -= j / 2;
 		hex[j++] = ' ';
 
 		seq_buf_putmem(s, hex, j);
 		if (seq_buf_has_overflowed(s))
 			return -1;
+
+		len -= start_len;
+		data += start_len;
 	}
 	return 0;
 }
-- 
2.26.1