Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in bch2_stripe_to_text

[Zhao Mengmeng]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 1ec6d097897aFrom fd481965777d8a4fa677ec8318d2562737b2d745 Mon Sep 17 00:00:00 2001
From: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
Date: Wed, 9 Oct 2024 11:18:04 +0800
Subject: [PATCH] bcachefs: Fix shift-out-of-bounds in bch2_stripe_to_text

syzbot report a shift-out-of-bounds issue:
------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/bcachefs/ec.c:147:2
shift exponent 108 is too large for 32-bit type 'unsigned int'
----
Here s.csum_granularity_bits = 108, so shift is impossible for unsigned
int. To fix, add a check in bch2_stripe_validate() to bail out, it has
same checking logic with ec_stripe_key_init().

Reported-by: syzbot+f8c98a50c323635be65d@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+f8c98a50c323635be65d@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=f8c98a50c323635be65d
Suggested-by: Hongbo Li <lihongbo22@xxxxxxxxxx>
Signed-off-by: Zhao Mengmeng <zhaomengmeng@xxxxxxxxxx>
---
 fs/bcachefs/ec.c      | 6 ++++++
 fs/bcachefs/errcode.h | 3 ++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
index 141a4c63142f..bc5ff1331c6f 100644
--- a/fs/bcachefs/ec.c
+++ b/fs/bcachefs/ec.c
@@ -113,6 +113,12 @@ int bch2_stripe_validate(struct bch_fs *c, struct bkey_s_c k,
 	const struct bch_stripe *s = bkey_s_c_to_stripe(k).v;
 	int ret = 0;
 
+	if (s->csum_granularity_bits >= ilog2(le16_to_cpu(s->sectors))) {
+		bch_err_ratelimited(c, "stripe csum gran bits %u too big",
+				    s->csum_granularity_bits);
+		return -BCH_ERR_stripe_csum_granularity_bits_too_big;
+	}
+
 	bkey_fsck_err_on(bkey_eq(k.k->p, POS_MIN) ||
 			 bpos_gt(k.k->p, POS(0, U32_MAX)),
 			 c, stripe_pos_bad,
diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
index 742dcdd3e5d7..14ba6bc7a029 100644
--- a/fs/bcachefs/errcode.h
+++ b/fs/bcachefs/errcode.h
@@ -258,7 +258,8 @@
 	x(BCH_ERR_nopromote,		nopromote_no_writes)			\
 	x(BCH_ERR_nopromote,		nopromote_enomem)			\
 	x(0,				invalid_snapshot_node)			\
-	x(0,				option_needs_open_fs)
+	x(0,				option_needs_open_fs)			\
+	x(EINVAL,			stripe_csum_granularity_bits_too_big)
 
 enum bch_errcode {
 	BCH_ERR_START		= 2048,
-- 
2.43.0