On 22/05/12 08:34PM, Wang Cheng wrote: > mpol_set_nodemask()(mm/mempolicy.c) does not set up nodemask when > pol->mode is MPOL_LOCAL. Check pol->mode before access > pol->w.cpuset_mems_allowed in mpol_rebind_policy()(mm/mempolicy.c). > > BUG: KMSAN: uninit-value in mpol_rebind_policy mm/mempolicy.c:352 [inline] > BUG: KMSAN: uninit-value in mpol_rebind_task+0x2ac/0x2c0 mm/mempolicy.c:368 > mpol_rebind_policy mm/mempolicy.c:352 [inline] > mpol_rebind_task+0x2ac/0x2c0 mm/mempolicy.c:368 > cpuset_change_task_nodemask kernel/cgroup/cpuset.c:1711 [inline] > cpuset_attach+0x787/0x15e0 kernel/cgroup/cpuset.c:2278 > cgroup_migrate_execute+0x1023/0x1d20 kernel/cgroup/cgroup.c:2515 > cgroup_migrate kernel/cgroup/cgroup.c:2771 [inline] > cgroup_attach_task+0x540/0x8b0 kernel/cgroup/cgroup.c:2804 > __cgroup1_procs_write+0x5cc/0x7a0 kernel/cgroup/cgroup-v1.c:520 > cgroup1_tasks_write+0x94/0xb0 kernel/cgroup/cgroup-v1.c:539 > cgroup_file_write+0x4c2/0x9e0 kernel/cgroup/cgroup.c:3852 > kernfs_fop_write_iter+0x66a/0x9f0 fs/kernfs/file.c:296 > call_write_iter include/linux/fs.h:2162 [inline] > new_sync_write fs/read_write.c:503 [inline] > vfs_write+0x1318/0x2030 fs/read_write.c:590 > ksys_write+0x28b/0x510 fs/read_write.c:643 > __do_sys_write fs/read_write.c:655 [inline] > __se_sys_write fs/read_write.c:652 [inline] > __x64_sys_write+0xdb/0x120 fs/read_write.c:652 > do_syscall_x64 arch/x86/entry/common.c:51 [inline] > do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Uninit was created at: > slab_post_alloc_hook mm/slab.h:524 [inline] > slab_alloc_node mm/slub.c:3251 [inline] > slab_alloc mm/slub.c:3259 [inline] > kmem_cache_alloc+0x902/0x11c0 mm/slub.c:3264 > mpol_new mm/mempolicy.c:293 [inline] > do_set_mempolicy+0x421/0xb70 mm/mempolicy.c:853 > kernel_set_mempolicy mm/mempolicy.c:1504 [inline] > __do_sys_set_mempolicy mm/mempolicy.c:1510 [inline] > __se_sys_set_mempolicy+0x44c/0xb60 mm/mempolicy.c:1507 > __x64_sys_set_mempolicy+0xd8/0x110 mm/mempolicy.c:1507 > do_syscall_x64 arch/x86/entry/common.c:51 [inline] > do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:82 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > KMSAN: uninit-value in mpol_rebind_task (2) > https://syzkaller.appspot.com/bug?id=d6eb90f952c2a5de9ea718a1b873c55cb13b59dc > > Reported-and-tested-by: syzbot+217f792c92599518a2ab@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Wang Cheng <wanngchenng@xxxxxxxxx> > --- > The uninit-value is pol->w.cpuset_mems_allowed in > mpol_rebind_policy(). > > While syzkaller reproducer runs, I notice pol->mode is 4(MPOL_LOCAL) in > mpol_set_nodemask() > do_set_mempolicy()(mm/mempolicy.c) > that `nodemask` in `pol` is not initialized, which will be accessed in > mpol_rebind_policy(). > > mm/mempolicy.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 10e9c87260ed..18b74f02da71 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -347,7 +347,7 @@ static void mpol_rebind_preferred(struct mempolicy *pol, > */ > static void mpol_rebind_policy(struct mempolicy *pol, const nodemask_t *newmask) > { > - if (!pol) > + if (!pol || pol->mode == MPOL_LOCAL) > return; > if (!mpol_store_user_nodemask(pol) && > nodes_equal(pol->w.cpuset_mems_allowed, *newmask)) > -- > 2.30.2 > Hi Andrew, Thank you for fixing the commit message. This patch seems to fix below bug too. KMSAN: uninit-value in mpol_rebind_mm (2) https://syzkaller.appspot.com/bug?id=f2fecd0d7013f54ec4162f60743a2b28df40926b The uninit-value is pol->w.cpuset_mems_allowed in mpol_rebind_policy(). When syzkaller reproducer runs to the beginning of mpol_new(), mpol_new() mm/mempolicy.c do_mbind() mm/mempolicy.c kernel_mbind() mm/mempolicy.c `mode` is 1(MPOL_PREFERRED), nodes_empty(*nodes) is `true` and `flags` is 0. Then mode = MPOL_LOCAL; ... policy->mode = mode; policy->flags = flags; will be executed. So in mpol_set_nodemask(), mpol_set_nodemask() mm/mempolicy.c do_mbind() kernel_mbind() pol->mode is 4(MPOL_LOCAL), that `nodemask` in `pol` is not initialized, which will be accessed in mpol_rebind_policy(). IIUC, "#syz fix: mm/mempolicy: fix uninit-value in mpol_rebind_policy()" could be sent to syzbot+ad1b8c404f0959c4bfcc@xxxxxxxxxxxxxxxxxxxxxxxxx to attach the fixing commit to the bug. WDYT? thanks, - w
