• Darrick J. Wong's avatar
    bcache: fix BUG_ON due to integer overflow with GC_SECTORS_USED · 94717447
    Darrick J. Wong authored
    The BUG_ON at the end of __bch_btree_mark_key can be triggered due to
    an integer overflow error:
    
    BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 13);
    ...
    SET_GC_SECTORS_USED(g, min_t(unsigned,
    	     GC_SECTORS_USED(g) + KEY_SIZE(k),
    	     (1 << 14) - 1));
    BUG_ON(!GC_SECTORS_USED(g));
    
    In bcache.h, the SECTORS_USED bitfield is defined to be 13 bits wide.
    While the SET_ code tries to ensure that the field doesn't overflow by
    clamping it to (1<<14)-1 == 16383, this is incorrect because 16383
    requires 14 bits.  Therefore, if GC_SECTORS_USED() + KEY_SIZE() =
    8192, the SET_ statement tries to store 8192 into a 13-bit field.  In
    a 13-bit field, 8192 becomes zero, thus triggering the BUG_ON.
    
    Therefore, create a field width constant and a max value constant, and
    use those to create the bitfield and check the inputs to
    SET_GC_SECTORS_USED.  Arguably the BITMASK() template ought to have
    BUG_ON checks for too-large values, but that's a separate patch.
    Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    94717447
bcache.h 29.2 KB