6.13-stable review patch. If anyone has any objections, please let me know.
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From: Liam R. Howlett Liam.Howlett@Oracle.com
[ Upstream commit 64c37e134b120fb462fb4a80694bfb8e7be77b14 ]
If a memory allocation fails during dup_mmap(), the maple tree can be left in an unsafe state for other iterators besides the exit path. All the locks are dropped before the exit_mmap() call (in mm/mmap.c), but the incomplete mm_struct can be reached through (at least) the rmap finding the vmas which have a pointer back to the mm_struct.
Up to this point, there have been no issues with being able to find an mm_struct that was only partially initialised. Syzbot was able to make the incomplete mm_struct fail with recent forking changes, so it has been proven unsafe to use the mm_struct that hasn't been initialised, as referenced in the link below.
Although 8ac662f5da19f ("fork: avoid inappropriate uprobe access to invalid mm") fixed the uprobe access, it does not completely remove the race.
This patch sets the MMF_OOM_SKIP to avoid the iteration of the vmas on the oom side (even though this is extremely unlikely to be selected as an oom victim in the race window), and sets MMF_UNSTABLE to avoid other potential users from using a partially initialised mm_struct.
When registering vmas for uprobe, skip the vmas in an mm that is marked unstable. Modifying a vma in an unstable mm may cause issues if the mm isn't fully initialised.
Link: https://lore.kernel.org/all/6756d273.050a0220.2477f.003d.GAE@google.com/ Link: https://lkml.kernel.org/r/20250127170221.1761366-1-Liam.Howlett@oracle.com Fixes: d24062914837 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()") Signed-off-by: Liam R. Howlett Liam.Howlett@Oracle.com Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Oleg Nesterov oleg@redhat.com Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Jann Horn jannh@google.com Cc: Peter Zijlstra peterz@infradead.org Cc: Michal Hocko mhocko@suse.com Cc: Peng Zhang zhangpeng.00@bytedance.com Cc: Matthew Wilcox willy@infradead.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/uprobes.c | 4 ++++ kernel/fork.c | 17 ++++++++++++++--- 2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 5d71ef85420c5..7f1a95b4f14de 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -28,6 +28,7 @@ #include <linux/rcupdate_trace.h> #include <linux/workqueue.h> #include <linux/srcu.h> +#include <linux/oom.h> /* check_stable_address_space */
#include <linux/uprobes.h>
@@ -1260,6 +1261,9 @@ register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new) * returns NULL in find_active_uprobe_rcu(). */ mmap_write_lock(mm); + if (check_stable_address_space(mm)) + goto unlock; + vma = find_vma(mm, info->vaddr); if (!vma || !valid_vma(vma, is_register) || file_inode(vma->vm_file) != uprobe->inode) diff --git a/kernel/fork.c b/kernel/fork.c index 9b301180fd416..9da032802e347 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -760,7 +760,8 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, mt_set_in_rcu(vmi.mas.tree); ksm_fork(mm, oldmm); khugepaged_fork(mm, oldmm); - } else if (mpnt) { + } else { + /* * The entire maple tree has already been duplicated. If the * mmap duplication fails, mark the failure point with @@ -768,8 +769,18 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm, * stop releasing VMAs that have not been duplicated after this * point. */ - mas_set_range(&vmi.mas, mpnt->vm_start, mpnt->vm_end - 1); - mas_store(&vmi.mas, XA_ZERO_ENTRY); + if (mpnt) { + mas_set_range(&vmi.mas, mpnt->vm_start, mpnt->vm_end - 1); + mas_store(&vmi.mas, XA_ZERO_ENTRY); + /* Avoid OOM iterating a broken tree */ + set_bit(MMF_OOM_SKIP, &mm->flags); + } + /* + * The mm_struct is going to exit, but the locks will be dropped + * first. Set the mm_struct as unstable is advisable as it is + * not fully initialised. + */ + set_bit(MMF_UNSTABLE, &mm->flags); } out: mmap_write_unlock(mm);