From aca19e063b5126aab797f5739faaf3ddc82bd587 Mon Sep 17 00:00:00 2001 From: Jan Engelhardt Date: Fri, 18 Jul 2014 20:00:27 +0200 Subject: [PATCH] Do not attempt access beyond the declared end of the dn_blkptr array This loop in dmu_objset_write_ready(): for (i = 0; i < dnp->dn_nblkptr; i++) bp->blk_fill += dnp->dn_blkptr[i].blk_fill; invokes _undefined behavior_ for the (common) case of dn_nblkptr=3, therefore, the compiler is free to do whatever it wants (such as optimizing it away, or otherwise messing up your expections). The fix is to be honest about the array size. Signed-off-by: Tim Chase Signed-off-by: Brian Behlendorf Closes #2511 Closes #2010 --- include/sys/dnode.h | 28 +++++++++++++++++++++++++--- 1 file changed, 25 insertions(+), 3 deletions(-) diff --git a/include/sys/dnode.h b/include/sys/dnode.h index 55b87bc394ff..fa0aa4bb7a98 100644 --- a/include/sys/dnode.h +++ b/include/sys/dnode.h @@ -138,9 +138,31 @@ typedef struct dnode_phys { uint64_t dn_pad3[4]; - blkptr_t dn_blkptr[1]; - uint8_t dn_bonus[DN_MAX_BONUSLEN - sizeof (blkptr_t)]; - blkptr_t dn_spill; + /* + * The tail region is 448 bytes, and there are three ways to + * look at it. + * + * 0 64 128 192 256 320 384 448 (offset) + * +---------------+---------------+---------------+-------+ + * | dn_blkptr[0] | dn_blkptr[1] | dn_blkptr[2] | / | + * +---------------+---------------+---------------+-------+ + * | dn_blkptr[0] | dn_bonus[0..319] | + * +---------------+-----------------------+---------------+ + * | dn_blkptr[0] | / | dn_spill | + * +---------------+-----------------------+---------------+ + */ + union { + blkptr_t dn_blkptr[1+DN_MAX_BONUSLEN/sizeof (blkptr_t)]; + struct { + blkptr_t __dn_ignore1; + uint8_t dn_bonus[DN_MAX_BONUSLEN]; + }; + struct { + blkptr_t __dn_ignore2; + uint8_t __dn_ignore3[DN_MAX_BONUSLEN-sizeof (blkptr_t)]; + blkptr_t dn_spill; + }; + }; } dnode_phys_t; typedef struct dnode {