damos_new_filter() is returning a damos_filter struct without initializing its ->list field. And the users of the function uses the struct without initializing the field. As a result, uninitialized memory access error is possible. Actually, a kernel NULL pointer dereference BUG can be triggered using DAMON user-space tool, like below.
# damo start --damos_action stat --damos_filter anon matching # damo tune --damos_action stat --damos_filter anon matching --damos_filter anon nomatching # dmesg [...] [ 36.908136] BUG: kernel NULL pointer dereference, address: 0000000000000008 [ 36.910483] #PF: supervisor write access in kernel mode [ 36.912238] #PF: error_code(0x0002) - not-present page [ 36.913415] PGD 0 P4D 0 [ 36.913978] Oops: 0002 [#1] PREEMPT SMP PTI [ 36.914878] CPU: 32 PID: 1335 Comm: kdamond.0 Not tainted 6.5.0-rc3-mm-unstable-damon+ #1 [ 36.916621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 [ 36.919051] RIP: 0010:damos_destroy_filter (include/linux/list.h:114 include/linux/list.h:137 include/linux/list.h:148 mm/damon/core.c:345 mm/damon/core.c:355) [...] [ 36.938247] Call Trace: [ 36.938721] <TASK> [...] [ 36.950064] ? damos_destroy_filter (include/linux/list.h:114 include/linux/list.h:137 include/linux/list.h:148 mm/damon/core.c:345 mm/damon/core.c:355) [ 36.950883] ? damon_sysfs_set_scheme_filters.isra.0 (mm/damon/sysfs-schemes.c:1573) [ 36.952019] damon_sysfs_set_schemes (mm/damon/sysfs-schemes.c:1674 mm/damon/sysfs-schemes.c:1686) [ 36.952875] damon_sysfs_apply_inputs (mm/damon/sysfs.c:1312 mm/damon/sysfs.c:1298) [ 36.953757] ? damon_pa_check_accesses (mm/damon/paddr.c:168 mm/damon/paddr.c:179) [ 36.954648] damon_sysfs_cmd_request_callback (mm/damon/sysfs.c:1329 mm/damon/sysfs.c:1359) [...]
The first patch of this patchset fixes the bug by initializing the field in damos_new_filter(). The second patch adds a unit test for the problem. Note that the second patch Cc stable@ without Fixes: tag, since it would be better to be ingested together for avoiding any future regression.
SeongJae Park (2): mm/damon/core: initialize damo_filter->list from damos_new_filter() mm/damon/core-test: add a test for damos_new_filter()
mm/damon/core-test.h | 13 +++++++++++++ mm/damon/core.c | 1 + 2 files changed, 14 insertions(+)