linux-kernel - Re: [syzbot] [fs?] general protection fault in iter_file_splice

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Message-ID: <tencent_11C652F8465D499BEEC06EC00CAFE7D30606@qq.com>
Date: Wed, 22 May 2024 13:21:48 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+d2125fcb6aa8c4276fd2@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [fs?] general protection fault in iter_file_splice_write

please test null ptr in iter_file_splice_write

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 33e02dc69afb

diff --git a/fs/splice.c b/fs/splice.c
index 218e24b1ac40..1a3c31f3e63a 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -392,6 +392,7 @@ ssize_t copy_splice_read(struct file *in, loff_t *ppos,
 			.offset	= 0,
 			.len	= chunk,
 		};
+		printk("buf: %p, ops: %p, %s\n", buf, buf->ops, __func__);
 		pipe->head++;
 		remain -= chunk;
 	}
@@ -498,6 +499,7 @@ static inline bool eat_empty_buffer(struct pipe_inode_info *pipe)
 	unsigned int mask = pipe->ring_size - 1;
 	struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 
+	printk("buf: %p, ops: %p, tail: %d %s\n", buf, buf->ops, tail, __func__);
 	if (unlikely(!buf->len)) {
 		pipe_buf_release(pipe, buf);
 		pipe->tail = tail+1;
@@ -755,8 +757,11 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 			if (ret >= buf->len) {
 				ret -= buf->len;
-				buf->len = 0;
-				pipe_buf_release(pipe, buf);
+				printk("buf: %p, ops: %p, buf len: %d, tail: %d, ret: %d, tl: %llu, %s\n", buf, buf->ops, buf->len, tail, ret, sd.total_len, __func__);
+				if (buf->len) {
+					buf->len = 0;
+					pipe_buf_release(pipe, buf);
+				}
 				tail++;
 				pipe->tail = tail;
 				if (pipe->files)
@@ -1483,6 +1488,7 @@ static ssize_t iter_to_pipe(struct iov_iter *from,
 					put_page(pages[i]);
 				goto out;
 			}
+			printk("buf: %p, size: %lu, left: %lu, total: %lu, ret: %lu, %s\n", buf, buf.len, left, total, ret, __func__);
 			total += ret;
 			left -= size;
 			start = 0;