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    Subject[PATCH 5.17 19/75] exfat: check if cluster num is valid
    Date
    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 | 6 ++++++
    fs/exfat/fatent.c | 6 ------
    3 files changed, 12 insertions(+), 8 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
    @@ -380,6 +380,12 @@ static inline int exfat_sector_to_cluste
    EXFAT_RESERVED_CLUSTERS;
    }

    +static inline bool is_valid_cluster(struct exfat_sb_info *sbi,
    + unsigned int clus)
    +{
    + return clus >= EXFAT_FIRST_CLUSTER && clus < sbi->num_clusters;
    +}
    +
    /* 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
    @@ -81,12 +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)
    -{
    - return clus >= EXFAT_FIRST_CLUSTER && clus < sbi->num_clusters;
    -}
    -
    int exfat_ent_get(struct super_block *sb, unsigned int loc,
    unsigned int *content)
    {

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