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    Subject[ 104/117] block: dont mark buffers beyond end of disk as mapped
    3.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jeff Moyer <jmoyer@redhat.com>

    commit 080399aaaf3531f5b8761ec0ac30ff98891e8686 upstream.

    Hi,

    We have a bug report open where a squashfs image mounted on ppc64 would
    exhibit errors due to trying to read beyond the end of the disk. It can
    easily be reproduced by doing the following:

    [root@ibm-p750e-02-lp3 ~]# ls -l install.img
    -rw-r--r-- 1 root root 142032896 Apr 30 16:46 install.img
    [root@ibm-p750e-02-lp3 ~]# mount -o loop ./install.img /mnt/test
    [root@ibm-p750e-02-lp3 ~]# dd if=/dev/loop0 of=/dev/null
    dd: reading `/dev/loop0': Input/output error
    277376+0 records in
    277376+0 records out
    142016512 bytes (142 MB) copied, 0.9465 s, 150 MB/s

    In dmesg, you'll find the following:

    squashfs: version 4.0 (2009/01/31) Phillip Lougher
    [ 43.106012] attempt to access beyond end of device
    [ 43.106029] loop0: rw=0, want=277410, limit=277408
    [ 43.106039] Buffer I/O error on device loop0, logical block 138704
    [ 43.106053] attempt to access beyond end of device
    [ 43.106057] loop0: rw=0, want=277412, limit=277408
    [ 43.106061] Buffer I/O error on device loop0, logical block 138705
    [ 43.106066] attempt to access beyond end of device
    [ 43.106070] loop0: rw=0, want=277414, limit=277408
    [ 43.106073] Buffer I/O error on device loop0, logical block 138706
    [ 43.106078] attempt to access beyond end of device
    [ 43.106081] loop0: rw=0, want=277416, limit=277408
    [ 43.106085] Buffer I/O error on device loop0, logical block 138707
    [ 43.106089] attempt to access beyond end of device
    [ 43.106093] loop0: rw=0, want=277418, limit=277408
    [ 43.106096] Buffer I/O error on device loop0, logical block 138708
    [ 43.106101] attempt to access beyond end of device
    [ 43.106104] loop0: rw=0, want=277420, limit=277408
    [ 43.106108] Buffer I/O error on device loop0, logical block 138709
    [ 43.106112] attempt to access beyond end of device
    [ 43.106116] loop0: rw=0, want=277422, limit=277408
    [ 43.106120] Buffer I/O error on device loop0, logical block 138710
    [ 43.106124] attempt to access beyond end of device
    [ 43.106128] loop0: rw=0, want=277424, limit=277408
    [ 43.106131] Buffer I/O error on device loop0, logical block 138711
    [ 43.106135] attempt to access beyond end of device
    [ 43.106139] loop0: rw=0, want=277426, limit=277408
    [ 43.106143] Buffer I/O error on device loop0, logical block 138712
    [ 43.106147] attempt to access beyond end of device
    [ 43.106151] loop0: rw=0, want=277428, limit=277408
    [ 43.106154] Buffer I/O error on device loop0, logical block 138713
    [ 43.106158] attempt to access beyond end of device
    [ 43.106162] loop0: rw=0, want=277430, limit=277408
    [ 43.106166] attempt to access beyond end of device
    [ 43.106169] loop0: rw=0, want=277432, limit=277408
    ...
    [ 43.106307] attempt to access beyond end of device
    [ 43.106311] loop0: rw=0, want=277470, limit=2774

    Squashfs manages to read in the end block(s) of the disk during the
    mount operation. Then, when dd reads the block device, it leads to
    block_read_full_page being called with buffers that are beyond end of
    disk, but are marked as mapped. Thus, it would end up submitting read
    I/O against them, resulting in the errors mentioned above. I fixed the
    problem by modifying init_page_buffers to only set the buffer mapped if
    it fell inside of i_size.

    Cheers,
    Jeff

    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
    Acked-by: Nick Piggin <npiggin@kernel.dk>

    --

    Changes from v1->v2: re-used max_block, as suggested by Nick Piggin.
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/block_dev.c | 6 +++---
    fs/buffer.c | 4 +++-
    include/linux/fs.h | 1 +
    3 files changed, 7 insertions(+), 4 deletions(-)

    diff --git a/fs/block_dev.c b/fs/block_dev.c
    index e08f6a20..ba11c30 100644
    --- a/fs/block_dev.c
    +++ b/fs/block_dev.c
    @@ -70,7 +70,7 @@ static void bdev_inode_switch_bdi(struct inode *inode,
    spin_unlock(&dst->wb.list_lock);
    }

    -static sector_t max_block(struct block_device *bdev)
    +sector_t blkdev_max_block(struct block_device *bdev)
    {
    sector_t retval = ~((sector_t)0);
    loff_t sz = i_size_read(bdev->bd_inode);
    @@ -163,7 +163,7 @@ static int
    blkdev_get_block(struct inode *inode, sector_t iblock,
    struct buffer_head *bh, int create)
    {
    - if (iblock >= max_block(I_BDEV(inode))) {
    + if (iblock >= blkdev_max_block(I_BDEV(inode))) {
    if (create)
    return -EIO;

    @@ -185,7 +185,7 @@ static int
    blkdev_get_blocks(struct inode *inode, sector_t iblock,
    struct buffer_head *bh, int create)
    {
    - sector_t end_block = max_block(I_BDEV(inode));
    + sector_t end_block = blkdev_max_block(I_BDEV(inode));
    unsigned long max_blocks = bh->b_size >> inode->i_blkbits;

    if ((iblock + max_blocks) > end_block) {
    diff --git a/fs/buffer.c b/fs/buffer.c
    index 351e18e..ad5938c 100644
    --- a/fs/buffer.c
    +++ b/fs/buffer.c
    @@ -921,6 +921,7 @@ init_page_buffers(struct page *page, struct block_device *bdev,
    struct buffer_head *head = page_buffers(page);
    struct buffer_head *bh = head;
    int uptodate = PageUptodate(page);
    + sector_t end_block = blkdev_max_block(I_BDEV(bdev->bd_inode));

    do {
    if (!buffer_mapped(bh)) {
    @@ -929,7 +930,8 @@ init_page_buffers(struct page *page, struct block_device *bdev,
    bh->b_blocknr = block;
    if (uptodate)
    set_buffer_uptodate(bh);
    - set_buffer_mapped(bh);
    + if (block < end_block)
    + set_buffer_mapped(bh);
    }
    block++;
    bh = bh->b_this_page;
    diff --git a/include/linux/fs.h b/include/linux/fs.h
    index 8de6755..25c40b9 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -2051,6 +2051,7 @@ extern void unregister_blkdev(unsigned int, const char *);
    extern struct block_device *bdget(dev_t);
    extern struct block_device *bdgrab(struct block_device *bdev);
    extern void bd_set_size(struct block_device *, loff_t size);
    +extern sector_t blkdev_max_block(struct block_device *bdev);
    extern void bd_forget(struct inode *inode);
    extern void bdput(struct block_device *);
    extern void invalidate_bdev(struct block_device *);



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