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... 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 :) > 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. thanks, greg k-h
