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
Add checks to validate if cluster number is within valid range in exfat_clear_bitmap() and exfat_set_bitmap()
Cc: Namjae Jeon linkinjeon@kernel.org Cc: Sungjong Seo sj1557.seo@samsung.com Cc: linux-fsdevel@vger.kernel.org Cc: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?id=50381fc73821ecae743b8cf24b4c9a04776f767... Reported-by: syzbot+a4087e40b9c13aad7892@syzkaller.appspotmail.com Fixes: 1e49a94cf707 ("exfat: add bitmap operations") Signed-off-by: Tadeusz Struk tadeusz.struk@linaro.org --- v2: - Use is_valid_cluster() helper to validate clu --- fs/exfat/balloc.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c index 03f142307174..92f5b5b5a0d0 100644 --- a/fs/exfat/balloc.c +++ b/fs/exfat/balloc.c @@ -149,6 +149,9 @@ int exfat_set_bitmap(struct inode *inode, unsigned int clu, bool sync) 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); @@ -167,6 +170,9 @@ void exfat_clear_bitmap(struct inode *inode, unsigned int clu, bool sync) 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);