On Wed, 29 Mar 2023 18:53:30 +0400 Ivan Orlov <ivan.orlov0322@xxxxxxxxx> wrote: > Syzkaller reported the following issue: > > ... > > The 'xas_store' call during page cache scanning can potentially > translate 'xas' into the error state (with the reproducer provided > by the syzkaller the error code is -ENOMEM). However, there are no > further checks after the 'xas_store', and the next call of 'xas_next' > at the start of the scanning cycle doesn't increase the xa_index, > and the issue occurs. > > This patch will add the xarray state error checking after the > 'xas_store' and the corresponding result error code. > > Tested via syzbot. > > Reported-by: syzbot+9578faa5475acb35fa50@xxxxxxxxxxxxxxxxxxxxxxxxx > Link: https://syzkaller.appspot.com/bug?id=7d6bb3760e026ece7524500fe44fb024a0e959fc > Signed-off-by: Ivan Orlov <ivan.orlov0322@xxxxxxxxx> > --- > mm/khugepaged.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 92e6f56a932d..4d9850d9ea7f 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -55,6 +55,7 @@ enum scan_result { > SCAN_CGROUP_CHARGE_FAIL, > SCAN_TRUNCATED, > SCAN_PAGE_HAS_PRIVATE, > + SCAN_STORE_FAILED, > }; > > #define CREATE_TRACE_POINTS > @@ -1840,6 +1841,15 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr, > goto xa_locked; > } > xas_store(&xas, hpage); > + if (xas_error(&xas)) { > + /* revert shmem_charge performed > + * in the previous condition > + */ > + mapping->nrpages--; > + shmem_uncharge(mapping->host, 1); > + result = SCAN_STORE_FAILED; > + goto xa_locked; > + } > nr_none++; > continue; > } Needs this, I assume. --- a/include/trace/events/huge_memory.h~mm-khugepaged-fix-kernel-bug-in-hpage_collapse_scan_file-fix +++ a/include/trace/events/huge_memory.h @@ -36,7 +36,8 @@ EM( SCAN_ALLOC_HUGE_PAGE_FAIL, "alloc_huge_page_failed") \ EM( SCAN_CGROUP_CHARGE_FAIL, "ccgroup_charge_failed") \ EM( SCAN_TRUNCATED, "truncated") \ - EMe(SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ + EM( SCAN_PAGE_HAS_PRIVATE, "page_has_private") \ + EMe(SCAN_STORE_FAILED, "store_failed") #undef EM #undef EMe _
