linux-kernel - Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in member_to

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Message-ID: <tencent_6ECC3C5D37B696EC36DE4A4C759B770B6709@qq.com>
Date: Tue,  3 Sep 2024 10:13:02 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+064ce437a1ad63d3f6ef@...kaller.appspotmail.com
Cc: kent.overstreet@...ux.dev,
	linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in member_to_text

Because the value of m.btree_bitmap_shift is 69 in this case, it cause 
shift-out-of-bounds in member_to_text.

Add a check for btree_bitmap_shift in validate_member, when it bigger than 64
return -BCH_ERR_invalid_sb_members.
Simultaneously adjust the output mode of btree_bitmap_shift in member_to_text. 

#syz test

diff --git a/fs/bcachefs/sb-members.c b/fs/bcachefs/sb-members.c
index 39196f2a4197..85a4245ea6a3 100644
--- a/fs/bcachefs/sb-members.c
+++ b/fs/bcachefs/sb-members.c
@@ -162,6 +162,12 @@ static int validate_member(struct printbuf *err,
 		return -BCH_ERR_invalid_sb_members;
 	}
 
+	if (m.btree_bitmap_shift > 64) {
+		prt_printf(err, "device %u: too many big bitmap shift (got %u, max 64)",
+			   i, m.btree_bitmap_shift);
+		return -BCH_ERR_invalid_sb_members;
+	}
+
 	return 0;
 }
 
@@ -245,8 +251,7 @@ static void member_to_text(struct printbuf *out,
 		prt_printf(out, "(none)");
 	prt_newline(out);
 
-	prt_printf(out, "Btree allocated bitmap blocksize:\t");
-	prt_units_u64(out, 1ULL << m.btree_bitmap_shift);
+	prt_printf(out, "Btree allocated bitmap shift: %d\t", m.btree_bitmap_shift);
 	prt_newline(out);
 
 	prt_printf(out, "Btree allocated bitmap:\t");