Dmitry Chestnykh wrote: > Hello, > > In ffs_inode_alloc(), inode generation numbers are incremented after > being assigned an initial random value. Since the di_gen field is a > signed integer, it may overflow, causing undefined behavior (this is > unlikely to ever happen, though). > > This patch always assigns a random non-zero positive integer in [1, > INT_MAX] range, not equal to the previous generation number.
will this cause problems if a number repeats? we've seen problems with that before, where you get a sequence like 4, 7, 4 and then bad things happen. > > -- > Dmitry Chestnykh > https://www.codingrobots.com > > > Index: src/sys/ufs/ffs/ffs_alloc.c > =================================================================== > RCS file: /cvs/src/sys/ufs/ffs/ffs_alloc.c,v > retrieving revision 1.108 > diff -u -p -u -r1.108 ffs_alloc.c > --- src/sys/ufs/ffs/ffs_alloc.c 23 May 2016 20:47:49 -0000 1.108 > +++ src/sys/ufs/ffs/ffs_alloc.c 24 Jun 2017 19:25:04 -0000 > @@ -361,6 +361,7 @@ ffs_inode_alloc(struct inode *pip, mode_ > struct inode *ip; > ufsino_t ino, ipref; > int cg, error; > + int32_t ngen; > > *vpp = NULL; > fs = pip->i_fs; > @@ -413,16 +414,12 @@ ffs_inode_alloc(struct inode *pip, mode_ > > /* > * Set up a new generation number for this inode. > - * XXX - just increment for now, this is wrong! (millert) > - * Need a way to preserve randomization. > */ > - if (DIP(ip, gen) != 0) > - DIP_ADD(ip, gen, 1); > - if (DIP(ip, gen) == 0) > - DIP_ASSIGN(ip, gen, arc4random() & INT_MAX); > - > - if (DIP(ip, gen) == 0 || DIP(ip, gen) == -1) > - DIP_ASSIGN(ip, gen, 1); /* Shouldn't happen */ > + do { > + ngen = arc4random_uniform(INT_MAX) + 1; > + } while (DIP(ip, gen) == ngen); > + > + DIP_ASSIGN(ip, gen, ngen); > > return (0); >
