6.15-stable review patch. If anyone has any objections, please let me know.
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From: Lorenzo Stoakes lorenzo.stoakes@oracle.com
commit 0cf4b1687a187ba9247c71721d8b064634eda1f7 upstream.
While an OOM failure in commit_merge() isn't really feasible due to the allocation which might fail (a maple tree pre-allocation) being 'too small to fail', we do need to handle this case correctly regardless.
In vma_merge_existing_range(), we can theoretically encounter failures which result in an OOM error in two ways - firstly dup_anon_vma() might fail with an OOM error, and secondly commit_merge() failing, ultimately, to pre-allocate a maple tree node.
The abort logic for dup_anon_vma() resets the VMA iterator to the initial range, ensuring that any logic looping on this iterator will correctly proceed to the next VMA.
However the commit_merge() abort logic does not do the same thing. This resulted in a syzbot report occurring because mlockall() iterates through VMAs, is tolerant of errors, but ended up with an incorrect previous VMA being specified due to incorrect iterator state.
While making this change, it became apparent we are duplicating logic - the logic introduced in commit 41e6ddcaa0f1 ("mm/vma: add give_up_on_oom option on modify/merge, use in uffd release") duplicates the vmg->give_up_on_oom check in both abort branches.
Additionally, we observe that we can perform the anon_dup check safely on dup_anon_vma() failure, as this will not be modified should this call fail.
Finally, we need to reset the iterator in both cases, so now we can simply use the exact same code to abort for both.
We remove the VM_WARN_ON(err != -ENOMEM) as it would be silly for this to be otherwise and it allows us to implement the abort check more neatly.
Link: https://lkml.kernel.org/r/20250606125032.164249-1-lorenzo.stoakes@oracle.com Fixes: 47b16d0462a4 ("mm: abort vma_modify() on merge out of memory failure") Signed-off-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Reported-by: syzbot+d16409ea9ecc16ed261a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/6842cc67.a00a0220.29ac89.003b.GAE@google.co... Reviewed-by: Pedro Falcato pfalcato@suse.de Reviewed-by: Vlastimil Babka vbabka@suse.cz Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Cc: Jann Horn jannh@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/vma.c | 22 ++++------------------ 1 file changed, 4 insertions(+), 18 deletions(-)
--- a/mm/vma.c +++ b/mm/vma.c @@ -927,26 +927,9 @@ static __must_check struct vm_area_struc err = dup_anon_vma(next, middle, &anon_dup); }
- if (err) + if (err || commit_merge(vmg)) goto abort;
- err = commit_merge(vmg); - if (err) { - VM_WARN_ON(err != -ENOMEM); - - if (anon_dup) - unlink_anon_vmas(anon_dup); - - /* - * We've cleaned up any cloned anon_vma's, no VMAs have been - * modified, no harm no foul if the user requests that we not - * report this and just give up, leaving the VMAs unmerged. - */ - if (!vmg->give_up_on_oom) - vmg->state = VMA_MERGE_ERROR_NOMEM; - return NULL; - } - khugepaged_enter_vma(vmg->target, vmg->flags); vmg->state = VMA_MERGE_SUCCESS; return vmg->target; @@ -955,6 +938,9 @@ abort: vma_iter_set(vmg->vmi, start); vma_iter_load(vmg->vmi);
+ if (anon_dup) + unlink_anon_vmas(anon_dup); + /* * This means we have failed to clone anon_vma's correctly, but no * actual changes to VMAs have occurred, so no harm no foul - if the