exfat: check if cluster num is valid

commit 64ba4b1 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: 1e49a94 ("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>
xanmod · Jun 6, 2022 · c504167 · c504167
1 parent 195fffb
commit c504167
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Showing 3 changed files with 14 additions and 10 deletions.
diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
@@ -148,7 +148,9 @@ int exfat_set_bitmap(struct inode *inode, unsigned int clu, bool sync)
 	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 *inode, unsigned int clu, bool sync)
 	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);

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
@@ -381,6 +381,14 @@ static inline int exfat_sector_to_cluster(struct exfat_sb_info *sbi,
 		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);

diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
@@ -81,14 +81,6 @@ int exfat_ent_set(struct super_block *sb, unsigned int loc,
 	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)
 {