[PATCH] bcachefs: Fix invalid shift in validate_sb_layout()

[Gianfranco Trad <gianf.trad@gmail.com>]

Add check on layout->sb_max_size_bits against BCH_SB_LAYOUT_SIZE_BITS_MAX
to prevent UBSAN shift-out-of-bounds in validate_sb_layout().

Reported-by: syzbot+089fad5a3a5e77825426@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=089fad5a3a5e77825426
Fixes: 03ef80b469d5 ("bcachefs: Ignore unknown mount options")
Tested-by: syzbot+089fad5a3a5e77825426@syzkaller.appspotmail.com
Signed-off-by: Gianfranco Trad <gianf.trad@gmail.com>
---
 fs/bcachefs/errcode.h  | 1 +
 fs/bcachefs/super-io.c | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
index 649263516ab1..b6cbd716000b 100644
--- a/fs/bcachefs/errcode.h
+++ b/fs/bcachefs/errcode.h
@@ -222,6 +222,7 @@
 	x(BCH_ERR_invalid_sb_layout,	invalid_sb_layout_type)			\
 	x(BCH_ERR_invalid_sb_layout,	invalid_sb_layout_nr_superblocks)	\
 	x(BCH_ERR_invalid_sb_layout,	invalid_sb_layout_superblocks_overlap)	\
+	x(BCH_ERR_invalid_sb_layout,    invalid_sb_layout_sb_max_size_bits)     \
 	x(BCH_ERR_invalid_sb,		invalid_sb_members_missing)		\
 	x(BCH_ERR_invalid_sb,		invalid_sb_members)			\
 	x(BCH_ERR_invalid_sb,		invalid_sb_disk_groups)			\
diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index ce7410d72089..44d0ac9b00dd 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -287,6 +287,11 @@ static int validate_sb_layout(struct bch_sb_layout *layout, struct printbuf *out
 		return -BCH_ERR_invalid_sb_layout_nr_superblocks;
 	}
 
+	if (layout->sb_max_size_bits > BCH_SB_LAYOUT_SIZE_BITS_MAX) {
+		prt_printf(out, "Invalid superblock layout: max_size_bits too high");
+		return -BCH_ERR_invalid_sb_layout_sb_max_size_bits;
+	}
+
 	max_sectors = 1 << layout->sb_max_size_bits;
 
 	prev_offset = le64_to_cpu(layout->sb_offset[0]);
-- 
2.43.0