Upstream commit: 64ba4b15e5c0 ("exfat: check if cluster num is valid")

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=50381fc73821ecae743b8cf24b4c9a04776f767... 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 --- fs/exfat/balloc.c | 8 ++++++-- fs/exfat/exfat_fs.h | 8 ++++++++ fs/exfat/fatent.c | 8 -------- 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c index cc5cffc4a769..e2113e0a848c 100644 --- 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 index 1d6da61157c9..9f82a8a835ee 100644 --- 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 index e949e563443c..421c27353104 100644 --- 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) {