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    Subject[PATCH 5.19 110/158] loop: Check for overflow while configuring loop
    Date
    From: Siddh Raman Pant <code@siddh.me>

    commit c490a0b5a4f36da3918181a8acdc6991d967c5f3 upstream.

    The userspace can configure a loop using an ioctl call, wherein
    a configuration of type loop_config is passed (see lo_ioctl()'s
    case on line 1550 of drivers/block/loop.c). This proceeds to call
    loop_configure() which in turn calls loop_set_status_from_info()
    (see line 1050 of loop.c), passing &config->info which is of type
    loop_info64*. This function then sets the appropriate values, like
    the offset.

    loop_device has lo_offset of type loff_t (see line 52 of loop.c),
    which is typdef-chained to long long, whereas loop_info64 has
    lo_offset of type __u64 (see line 56 of include/uapi/linux/loop.h).

    The function directly copies offset from info to the device as
    follows (See line 980 of loop.c):
    lo->lo_offset = info->lo_offset;

    This results in an overflow, which triggers a warning in iomap_iter()
    due to a call to iomap_iter_done() which has:
    WARN_ON_ONCE(iter->iomap.offset > iter->pos);

    Thus, check for negative value during loop_set_status_from_info().

    Bug report: https://syzkaller.appspot.com/bug?id=c620fe14aac810396d3c3edc9ad73848bf69a29e

    Reported-and-tested-by: syzbot+a8e049cd3abd342936b6@syzkaller.appspotmail.com
    Cc: stable@vger.kernel.org
    Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Signed-off-by: Siddh Raman Pant <code@siddh.me>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Link: https://lore.kernel.org/r/20220823160810.181275-1-code@siddh.me
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/block/loop.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- a/drivers/block/loop.c
    +++ b/drivers/block/loop.c
    @@ -979,6 +979,11 @@ loop_set_status_from_info(struct loop_de

    lo->lo_offset = info->lo_offset;
    lo->lo_sizelimit = info->lo_sizelimit;
    +
    + /* loff_t vars have been assigned __u64 */
    + if (lo->lo_offset < 0 || lo->lo_sizelimit < 0)
    + return -EOVERFLOW;
    +
    memcpy(lo->lo_file_name, info->lo_file_name, LO_NAME_SIZE);
    lo->lo_file_name[LO_NAME_SIZE-1] = 0;
    lo->lo_flags = info->lo_flags;

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