[PATCH 5.15 17/66] exfat: check if cluster num is valid

Greg Kroah-Hartman
2022-06-03T17:58:01Z

From: Tadeusz Struk <tadeusz.struk@linaro.org>

commit 64ba4b15e5c045f8b746c6da5fc9be9a6b00b61d upstream.

Syzbot reported slab-out-of-bounds read in exfat_clear_bitmap.
This was triggered by reproducer calling truncute with size 0,
which causes the following trace:

BUG: KASAN: slab-out-of-bounds in exfat_clear_bitmap+0x147/0x490 fs/exfat/balloc.c:174
Read of size 8 at addr ffff888115aa9508 by task syz-executor251/365

Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack_lvl+0x1e2/0x24b lib/dump_stack.c:118
print_address_description+0x81/0x3c0 mm/kasan/report.c:233
__kasan_report mm/kasan/report.c:419 [inline]
kasan_report+0x1a4/0x1f0 mm/kasan/report.c:436
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
exfat_clear_bitmap+0x147/0x490 fs/exfat/balloc.c:174
exfat_free_cluster+0x25a/0x4a0 fs/exfat/fatent.c:181
__exfat_truncate+0x99e/0xe00 fs/exfat/file.c:217
exfat_truncate+0x11b/0x4f0 fs/exfat/file.c:243
exfat_setattr+0xa03/0xd40 fs/exfat/file.c:339
notify_change+0xb76/0xe10 fs/attr.c:336
do_truncate+0x1ea/0x2d0 fs/open.c:65

Move the is_valid_cluster() helper from fatent.c to a common
header to make it reusable in other *.c files. And add is_valid_cluster()
to validate if cluster number is within valid range in exfat_clear_bitmap()
and exfat_set_bitmap().

Link: https://syzkaller.appspot.com/bug?id=50381fc73821ecae743b8cf24b4c9a04776f767c
Reported-by: syzbot+a4087e40b9c13aad7892@syzkaller.appspotmail.com
Fixes: 1e49a94cf707 ("exfat: add bitmap operations")
Cc: stable@vger.kernel.org # v5.7+
Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/exfat/balloc.c | 8 ++++++--
fs/exfat/exfat_fs.h | 8 ++++++++
fs/exfat/fatent.c | 8 --------
3 files changed, 14 insertions(+), 10 deletions(-)

--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -148,7 +148,9 @@ int exfat_set_bitmap(struct inode *inode
struct super_block *sb = inode->i_sb;
struct exfat_sb_info *sbi = EXFAT_SB(sb);

- WARN_ON(clu < EXFAT_FIRST_CLUSTER);
+ if (!is_valid_cluster(sbi, clu))
+ return -EINVAL;
+
ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
@@ -166,7 +168,9 @@ void exfat_clear_bitmap(struct inode *in
struct exfat_sb_info *sbi = EXFAT_SB(sb);
struct exfat_mount_options *opts = &sbi->options;

- WARN_ON(clu < EXFAT_FIRST_CLUSTER);
+ if (!is_valid_cluster(sbi, clu))
+ return;
+
ent_idx = CLUSTER_TO_BITMAP_ENT(clu);
i = BITMAP_OFFSET_SECTOR_INDEX(sb, ent_idx);
b = BITMAP_OFFSET_BIT_IN_SECTOR(sb, ent_idx);
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -381,6 +381,14 @@ static inline int exfat_sector_to_cluste
EXFAT_RESERVED_CLUSTERS;
}

+static inline bool is_valid_cluster(struct exfat_sb_info *sbi,
+ unsigned int clus)
+{
+ if (clus < EXFAT_FIRST_CLUSTER || sbi->num_clusters <= clus)
+ return false;
+ return true;
+}
+
/* super.c */
int exfat_set_volume_dirty(struct super_block *sb);
int exfat_clear_volume_dirty(struct super_block *sb);
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -81,14 +81,6 @@ int exfat_ent_set(struct super_block *sb
return 0;
}

-static inline bool is_valid_cluster(struct exfat_sb_info *sbi,
- unsigned int clus)
-{
- if (clus < EXFAT_FIRST_CLUSTER || sbi->num_clusters <= clus)
- return false;
- return true;
-}
-
int exfat_ent_get(struct super_block *sb, unsigned int loc,
unsigned int *content)
{