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    Subject[017/141] fat: fix possible overflow for fat_clusters
    3.6.11.6 stable review patch.
    If anyone has any objections, please let me know.

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

    From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

    [ Upstream commit 7b92d03c3239f43e5b86c9cc9630f026d36ee995 ]

    Intermediate value of fat_clusters can be overflowed on 32bits arch.

    Reported-by: Krzysztof Strasburger <strasbur@chkw386.ch.pwr.wroc.pl>
    Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    fs/fat/inode.c | 15 ++++++++++++++-
    1 file changed, 14 insertions(+), 1 deletion(-)

    diff --git a/fs/fat/inode.c b/fs/fat/inode.c
    index 05e897f..ca5241f 100644
    --- a/fs/fat/inode.c
    +++ b/fs/fat/inode.c
    @@ -1212,6 +1212,19 @@ static int fat_read_root(struct inode *inode)
    return 0;
    }

    +static unsigned long calc_fat_clusters(struct super_block *sb)
    +{
    + struct msdos_sb_info *sbi = MSDOS_SB(sb);
    +
    + /* Divide first to avoid overflow */
    + if (sbi->fat_bits != 12) {
    + unsigned long ent_per_sec = sb->s_blocksize * 8 / sbi->fat_bits;
    + return ent_per_sec * sbi->fat_length;
    + }
    +
    + return sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
    +}
    +
    /*
    * Read the super block of an MS-DOS FS.
    */
    @@ -1409,7 +1422,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
    sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;

    /* check that FAT table does not overflow */
    - fat_clusters = sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
    + fat_clusters = calc_fat_clusters(sb);
    total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
    if (total_clusters > MAX_FAT(sb)) {
    if (!silent)
    --
    1.7.10.4



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