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

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Date: Wed, 22 May 2024 20:49:03 +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 60aed8de21f8..8ec408c40755 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -715,6 +715,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 		/* build the vector */
 		left = sd.total_len;
+		printk("total len: %lu, %s\n", left, __func__);
 		for (n = 0; !pipe_empty(head, tail) && left && n < nbufs; tail++) {
 			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 			size_t this_len = buf->len;
@@ -751,9 +752,16 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 		/* dismiss the fully eaten buffers, adjust the partial one */
 		tail = pipe->tail;
-		while (ret) {
+		printk("ret: %ld, nbufs: %d, %s\n", ret, nbufs, __func__);
+		n = 0;
+		while (ret > 0 && n < nbufs) {
 			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
-			if (ret >= buf->len) {
+			if (!buf->len) {
+				tail++;
+				continue;
+			}
+			printk("buf len: %lu, %s\n", buf->len, __func__);
+			if (ret >= (ssize_t)buf->len) {
 				ret -= buf->len;
 				buf->len = 0;
 				pipe_buf_release(pipe, buf);
@@ -766,6 +774,7 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 				buf->len -= ret;
 				ret = 0;
 			}
+			n++;
 		}
 	}
 done: