commit 270aa010620697fb27b8f892cc4e194bc2b7d134 upstream.
Patch series "mm/uffd: Fix vma merge/split", v2.
This series contains two patches that fix vma merge/split for userfaultfd on two separate issues.
Patch 1 fixes a regression since 6.1+ due to something we overlooked when converting to maple tree apis. The plan is we use patch 1 to replace the commit "2f628010799e (mm: userfaultfd: avoid passing an invalid range to vma_merge())" in mm-hostfixes-unstable tree if possible, so as to bring uffd vma operations back aligned with the rest code again.
Patch 2 fixes a long standing issue that vma can be left unmerged even if we can for either uffd register or unregister.
Many thanks to Lorenzo on either noticing this issue from the assert movement patch, looking at this problem, and also provided a reproducer on the unmerged vma issue [1].
[1] https://gist.github.com/lorenzo-stoakes/a11a10f5f479e7a977fc456331266e0e
This patch (of 2):
It seems vma merging with uffd paths is broken with either register/unregister, where right now we can feed wrong parameters to vma_merge() and it's found by recent patch which moved asserts upwards in vma_merge() by Lorenzo Stoakes:
https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/
It's possible that "start" is contained within vma but not clamped to its start. We need to convert this into either "cannot merge" case or "can merge" case 4 which permits subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA will be clamped to the start.
This patch will eliminate the report and make sure vma_merge() calls will become legal again.
One thing to mention is that the "Fixes: 29417d292bd0" below is there only to help explain where the warning can start to trigger, the real commit to fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the issue, but unfortunately we may want to keep it in Fixes too just to ease kernel backporters for easier tracking.
Link: https://lkml.kernel.org/r/20230517190916.3429499-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20230517190916.3429499-2-peterx@redhat.com Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: Mark Rutland mark.rutland@arm.com Reviewed-by: Lorenzo Stoakes lstoakes@gmail.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/ Cc: Lorenzo Stoakes lstoakes@gmail.com Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: Liam R. Howlett Liam.Howlett@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Jakub Acs acsjakub@amazon.com [acsjakub: contextual change - keep call to mas_next()] Cc: linux-mm@kvack.org
--- This backport fixes a security issue - dangling pointer to a VMA in maple tree. Omitting details in this message to be brief, but happy to provide if requested.
Since the envelope mentions series fixes 2 separate issues I hope the patch is acceptable on its own?
fs/userfaultfd.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 82101a2cf933..fcf96f52b2e9 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1426,6 +1426,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, if (prev != vma) mas_next(&mas, ULONG_MAX);
+ if (vma->vm_start < start) + prev = vma; + ret = 0; do { cond_resched(); @@ -1603,6 +1606,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, if (prev != vma) mas_next(&mas, ULONG_MAX);
+ if (vma->vm_start < start) + prev = vma; + ret = 0; do { cond_resched();
Hi Jakub,
Subject: [PATCH 6.1] Mm/uffd: fix vma operation where start addr cuts part of vma
Nit: upstream commit has "mm/uffd...". The 'M' should be lowercase. Maybe your email client mangled the subject? Some of my tooling scans for commit subjects to track stable patches. So it would be nice to not change the subject without need.
On Wed, Jun 04 2025, Jakub Acs wrote:
commit 270aa010620697fb27b8f892cc4e194bc2b7d134 upstream.
[...]
-cc my personal mail
Hi Jakub,
I realise this is from an old report so totally forgivable :P but please use my work mail, everything that goes to my personal mail from the mailing lists is >/dev/null :)
I only noticed this because I was checking for something else ;)
The patch looks fine to me btw!
Cheers, Lorenzo
On Wed, Jun 04, 2025 at 12:38:30PM +0000, Jakub Acs wrote:
commit 270aa010620697fb27b8f892cc4e194bc2b7d134 upstream.
Patch series "mm/uffd: Fix vma merge/split", v2.
This series contains two patches that fix vma merge/split for userfaultfd on two separate issues.
Patch 1 fixes a regression since 6.1+ due to something we overlooked when converting to maple tree apis. The plan is we use patch 1 to replace the commit "2f628010799e (mm: userfaultfd: avoid passing an invalid range to vma_merge())" in mm-hostfixes-unstable tree if possible, so as to bring uffd vma operations back aligned with the rest code again.
Patch 2 fixes a long standing issue that vma can be left unmerged even if we can for either uffd register or unregister.
Many thanks to Lorenzo on either noticing this issue from the assert movement patch, looking at this problem, and also provided a reproducer on the unmerged vma issue [1].
[1] https://gist.github.com/lorenzo-stoakes/a11a10f5f479e7a977fc456331266e0e
This patch (of 2):
It seems vma merging with uffd paths is broken with either register/unregister, where right now we can feed wrong parameters to vma_merge() and it's found by recent patch which moved asserts upwards in vma_merge() by Lorenzo Stoakes:
https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/
It's possible that "start" is contained within vma but not clamped to its start. We need to convert this into either "cannot merge" case or "can merge" case 4 which permits subdivision of prev by assigning vma to prev. As we loop, each subsequent VMA will be clamped to the start.
This patch will eliminate the report and make sure vma_merge() calls will become legal again.
One thing to mention is that the "Fixes: 29417d292bd0" below is there only to help explain where the warning can start to trigger, the real commit to fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the issue, but unfortunately we may want to keep it in Fixes too just to ease kernel backporters for easier tracking.
Link: https://lkml.kernel.org/r/20230517190916.3429499-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20230517190916.3429499-2-peterx@redhat.com Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: Mark Rutland mark.rutland@arm.com Reviewed-by: Lorenzo Stoakes lstoakes@gmail.com Reviewed-by: Liam R. Howlett Liam.Howlett@oracle.com Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/ Cc: Lorenzo Stoakes lstoakes@gmail.com Cc: Mike Rapoport (IBM) rppt@kernel.org Cc: Liam R. Howlett Liam.Howlett@oracle.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Jakub Acs acsjakub@amazon.com [acsjakub: contextual change - keep call to mas_next()] Cc: linux-mm@kvack.org
This backport fixes a security issue - dangling pointer to a VMA in maple tree. Omitting details in this message to be brief, but happy to provide if requested.
Since the envelope mentions series fixes 2 separate issues I hope the patch is acceptable on its own?
fs/userfaultfd.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 82101a2cf933..fcf96f52b2e9 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1426,6 +1426,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, if (prev != vma) mas_next(&mas, ULONG_MAX);
- if (vma->vm_start < start)
prev = vma;- ret = 0; do { cond_resched();
@@ -1603,6 +1606,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, if (prev != vma) mas_next(&mas, ULONG_MAX);
- if (vma->vm_start < start)
prev = vma;- ret = 0; do { cond_resched();
-- 2.47.1
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