[PATCH] f2fs: fix shift-out-of-bounds in f2fs_fill_super

[Yangtao Li]

syzbot reported a bug which could cause shift-out-of-bounds issue:

UBSAN: shift-out-of-bounds in fs/f2fs/super.c:4184:41
shift exponent 613 is too large for 64-bit type 'loff_t' (aka 'long long')
CPU: 1 PID: 5467 Comm: syz-executor.0 Not tainted 6.2.0-rc5-syzkaller #0
Hardware name: Google Compute Engine/Google Compute Engine,
	BIOS Google 01/12/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x290 lib/dump_stack.c:106
 ubsan_epilogue lib/ubsan.c:151 [inline]
 __ubsan_handle_shift_out_of_bounds+0x33d/0x3a0 lib/ubsan.c:321
 f2fs_fill_super+0x5518/0x6ee0 fs/f2fs/super.c:4184
 mount_bdev+0x26c/0x3a0 fs/super.c:1359
 legacy_get_tree+0xea/0x180 fs/fs_context.c:610
 vfs_get_tree+0x88/0x270 fs/super.c:1489
 do_new_mount+0x289/0xad0 fs/namespace.c:3145
 do_mount fs/namespace.c:3488 [inline]
 __do_sys_mount fs/namespace.c:3697 [inline]
 __se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3674
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 </TASK>

Since currently only 4kb block size is supported by f2fs,
let's use 4kb directly to avoid triggering UBSAN exception.

Reported-by: syzbot+fea4bcda5eb938ee88ed@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
---
 fs/f2fs/super.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index d8a65645ee48..41c2bbd3e719 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4174,8 +4174,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	if (err)
 		goto free_options;
 
-	sb->s_maxbytes = max_file_blocks(NULL) <<
-				le32_to_cpu(raw_super->log_blocksize);
+	/* Currently, support only 4KB block size */
+	sb->s_maxbytes = max_file_blocks(NULL) << F2FS_BLKSIZE_BITS;
 	sb->s_max_links = F2FS_LINK_MAX;
 
 	err = f2fs_setup_casefold(sbi);
-- 
2.25.1