On Tue, Jun 02, 2020 at 04:04:04PM +0200, Greg Kroah-Hartman wrote: > On Tue, Jun 02, 2020 at 05:10:35AM -0700, Matthew Wilcox wrote: > > On Tue, Jun 02, 2020 at 07:50:33PM +0800, Wang Hai wrote: > > > syzkaller reports for memory leak when kobject_init_and_add() > > > returns an error in the function sysfs_slab_add() [1] > > > > > > When this happened, the function kobject_put() is not called for the > > > corresponding kobject, which potentially leads to memory leak. > > > > > > This patch fixes the issue by calling kobject_put() even if > > > kobject_init_and_add() fails. > > > > I think this speaks to a deeper problem with kobject_init_and_add() > > -- the need to call kobject_put() if it fails is not readily apparent > > to most users. This same bug appears in the first three users of > > kobject_init_and_add() that I checked -- > > arch/ia64/kernel/topology.c > > drivers/firmware/dmi-sysfs.c > > drivers/firmware/efi/esrt.c > > drivers/scsi/iscsi_boot_sysfs.c > > > > Some do get it right -- > > arch/powerpc/kernel/cacheinfo.c > > drivers/gpu/drm/ttm/ttm_bo.c > > drivers/gpu/drm/ttm/ttm_memory.c > > drivers/infiniband/hw/mlx4/sysfs.c > > Why are random individual drivers calling kobject* functions? That > speaks to a larger problem here... There's around 120 callers in the kernel today ... large, indeed. > Anyway, yes, it's a tricky function, but the issue usually is that the > kobject is embedded in something else and if you call init_and_add() you > want to tear things down _before_ the final put happens. > > The good thing is, that function is really hard to get to fail except if > you abuse it with syzkaller :) Yes ;-) > > I'd argue that the current behaviour is wrong, that kobject_init_and_add() > > should call kobject_put() if the add fails. This would need a tree-wide > > audit. But somebody needs to do that anyway because based on my random > > sampling, half of the users currently get it wrong. > > As said above, this is "tricky", and might break things. My audit may not be correct then. The kobject_put() may be appropriately being called at a higher level rather than in the same function as the kobject_init_and_add().
