bcache: fix BUG_ON due to integer overflow with GC_SECTORS_USED

commit 947174476701fbc84ea8c7ec9664270f9d80b076 upstream.

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: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 754f4317748322e7450d69da9591b6b72aff6dc4..cf3f6f897f1bd06652ee4eb000860bb690d7608d 100644 (file)
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -209,7 +209,9 @@ BITMASK(GC_MARK,     struct bucket, gc_mark, 0, 2);
 #define GC_MARK_RECLAIMABLE    0
 #define GC_MARK_DIRTY          1
 #define GC_MARK_METADATA       2
-BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, 13);
+#define GC_SECTORS_USED_SIZE   13
+#define MAX_GC_SECTORS_USED    (~(~0ULL << GC_SECTORS_USED_SIZE))
+BITMASK(GC_SECTORS_USED, struct bucket, gc_mark, 2, GC_SECTORS_USED_SIZE);
 BITMASK(GC_MOVE, struct bucket, gc_mark, 15, 1);
 
 #include "journal.h"

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 31bb53fcc67a40806cf73659a596f98297d36128..7966ff827680e5f826917834b3ac50ccc1a26ea3 100644 (file)
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -1163,7 +1163,7 @@ uint8_t __bch_btree_mark_key(struct cache_set *c, int level, struct bkey *k)
                /* guard against overflow */
                SET_GC_SECTORS_USED(g, min_t(unsigned,
                                             GC_SECTORS_USED(g) + KEY_SIZE(k),
-                                            (1 << 14) - 1));
+                                            MAX_GC_SECTORS_USED));
 
                BUG_ON(!GC_SECTORS_USED(g));
        }