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Date: Sat, 26 Jun 2021 11:21:55 +0800
From: Yun Zhou <yun.zhou@...driver.com>
To: <rostedt@...dmis.org>
CC: <linux-kernel@...r.kernel.org>, <kernel-hardening@...ts.openwall.com>,
<ying.xue@...driver.com>, <zhiquan.li@...driver.com>
Subject: [PATCH 1/2] seq_buf: fix overflow in seq_buf_putmem_hex()
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@...driver.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
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