| Message ID | tencent_0EBF9E731B704B091B022578BA9EBB8E3308@qq.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [next] btrfs: Accessing head_ref within delayed_refs lock | expand |
On Tue, Oct 15, 2024 at 1:40 PM Edward Adam Davis <eadavis@qq.com> wrote: > > This is because the thread routine btrfs_work_helper released head_def after > exiting delayed_refs->lock in add_delayed_ref. This should be explained a lot better. Starting the changelog with "This is because..." is odd. It should explain why the head reference was freed (because delayed references were run). > Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr > outside the delayed_refs->lock. > > Move head_ref->bytenr into the protection range of delayed_refs->lock > to avoid uaf in add_delayed_ref. This was already fixed yesterday, in a simpler way and with an explanation of what's going on to trigger the use-after-free: https://lore.kernel.org/linux-btrfs/02fc507b62b19be2348fc08de8b13bd7af1a440e.1728922973.git.fdmanana@suse.com/ Thanks. > > Fixes: a3aad8f4f5d9 ("btrfs: qgroups: remove bytenr field from struct btrfs_qgroup_extent_record") > Reported-and-tested-by: syzbot+c3a3a153f0190dca5be9@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9 > Signed-off-by: Edward Adam Davis <eadavis@qq.com> > --- > fs/btrfs/delayed-ref.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c > index 13c2e00d1270..f50fc05847a1 100644 > --- a/fs/btrfs/delayed-ref.c > +++ b/fs/btrfs/delayed-ref.c > @@ -1012,6 +1012,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, > int action = generic_ref->action; > bool merged; > int ret; > + u64 bytenr; > > node = kmem_cache_alloc(btrfs_delayed_ref_node_cachep, GFP_NOFS); > if (!node) > @@ -1056,6 +1057,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, > goto free_record; > } > head_ref = new_head_ref; > + bytenr = head_ref->bytenr; > > merged = insert_delayed_ref(trans, head_ref, node); > spin_unlock(&delayed_refs->lock); > @@ -1074,7 +1076,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, > kmem_cache_free(btrfs_delayed_ref_node_cachep, node); > > if (qrecord_inserted) > - return btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr); > + return btrfs_qgroup_trace_extent_post(trans, record, bytenr); > return 0; > > free_record: > -- > 2.43.0 > >
On Tue, Oct 15, 2024 at 01:49:04PM +0100, Filipe Manana wrote: > On Tue, Oct 15, 2024 at 1:40 PM Edward Adam Davis <eadavis@qq.com> wrote: > > > > This is because the thread routine btrfs_work_helper released head_def after > > exiting delayed_refs->lock in add_delayed_ref. > > This should be explained a lot better. Starting the changelog with > "This is because..." is odd. It should explain why the head reference > was freed (because delayed references were run). > > > Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr > > outside the delayed_refs->lock. > > > > Move head_ref->bytenr into the protection range of delayed_refs->lock > > to avoid uaf in add_delayed_ref. > > > This was already fixed yesterday, in a simpler way and with an > explanation of what's going on to trigger the use-after-free: > > https://lore.kernel.org/linux-btrfs/02fc507b62b19be2348fc08de8b13bd7af1a440e.1728922973.git.fdmanana@suse.com/ This will be in the upcoming linux-next, so we'll not get the syzbot and build reports anymore.
diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c index 13c2e00d1270..f50fc05847a1 100644 --- a/fs/btrfs/delayed-ref.c +++ b/fs/btrfs/delayed-ref.c @@ -1012,6 +1012,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, int action = generic_ref->action; bool merged; int ret; + u64 bytenr; node = kmem_cache_alloc(btrfs_delayed_ref_node_cachep, GFP_NOFS); if (!node) @@ -1056,6 +1057,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, goto free_record; } head_ref = new_head_ref; + bytenr = head_ref->bytenr; merged = insert_delayed_ref(trans, head_ref, node); spin_unlock(&delayed_refs->lock); @@ -1074,7 +1076,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans, kmem_cache_free(btrfs_delayed_ref_node_cachep, node); if (qrecord_inserted) - return btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr); + return btrfs_qgroup_trace_extent_post(trans, record, bytenr); return 0; free_record:
This is because the thread routine btrfs_work_helper released head_def after exiting delayed_refs->lock in add_delayed_ref. Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr outside the delayed_refs->lock. Move head_ref->bytenr into the protection range of delayed_refs->lock to avoid uaf in add_delayed_ref. Fixes: a3aad8f4f5d9 ("btrfs: qgroups: remove bytenr field from struct btrfs_qgroup_extent_record") Reported-and-tested-by: syzbot+c3a3a153f0190dca5be9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9 Signed-off-by: Edward Adam Davis <eadavis@qq.com> --- fs/btrfs/delayed-ref.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)