[PATCH v3] fs/ntfs3: validate BOOT sectors_per_clusters

[Randy Dunlap <rdunlap@infradead.org>]

When the NTFS BOOT sectors_per_clusters field is > 0x80,
it represents a shift value. Make sure that the shift value is
not too large before using it (NTFS max cluster size is 2MB).
Return -EVINVAL if it too large.

This prevents negative shift values and shift values that are
larger than the field size.

Prevents this UBSAN error:

 UBSAN: shift-out-of-bounds in ../fs/ntfs3/super.c:673:16
 shift exponent -192 is negative

Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: syzbot+1631f09646bc214d2e76@syzkaller.appspotmail.com
Cc: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Cc: ntfs3@lists.linux.dev
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kari Argillander <kari.argillander@stargateuniverse.net>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
---
v2: use Willy's suggestions
v3: use Namjae's suggestions -- but now Konstantin can decide.
    drop Willy's Rev-by: tag due to changes

 fs/ntfs3/super.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- linux-next-20220428.orig/fs/ntfs3/super.c
+++ linux-next-20220428/fs/ntfs3/super.c
@@ -668,9 +668,11 @@ static u32 format_size_gb(const u64 byte
 
 static u32 true_sectors_per_clst(const struct NTFS_BOOT *boot)
 {
-	return boot->sectors_per_clusters <= 0x80
-		       ? boot->sectors_per_clusters
-		       : (1u << (0 - boot->sectors_per_clusters));
+	if (boot->sectors_per_clusters <= 0x80)
+		return boot->sectors_per_clusters;
+	if (boot->sectors_per_clusters >= 0xf4) /* limit shift to 2MB max */
+		return 1U << (0 - boot->sectors_per_clusters);
+	return -EINVAL;
 }
 
 /*
@@ -713,6 +715,8 @@ static int ntfs_init_from_boot(struct su
 
 	/* cluster size: 512, 1K, 2K, 4K, ... 2M */
 	sct_per_clst = true_sectors_per_clst(boot);
+	if ((int)sct_per_clst < 0)
+		goto out;
 	if (!is_power_of_2(sct_per_clst))
 		goto out;