fix(objects): Make sure returned files can be used for purpose #279

flub · 2020-10-29T17:40:23Z

When the objects actor downloads files it ranks them and chooses the
highest ranking file. However before returning we must make sure the
file can actually be used for the requested purpose.

In particular this avoids asking for CFI but only getting a (64-bit)
PDB but no PE file. This file does not actually provide the requested
info, which then confuses the CfiActor because it tries to use it as a
CFI file, even though the file does not have CFI.

When the objects actor downloads files it ranks them and chooses the highest ranking file. However before returning we must make sure the file can actually be used for the requested purpose. In particular this avoids asking for CFI but only getting a (64-bit) PDB but no PE file. This file does not actually provide the requested info, which then confuses the CfiActor because it tries to use it as a CFI file, even though the file does not have CFI.

If there's an archive, but the file inside is malformed it was shown as simply missing. This fixes this to still give a malformed marker.

object_meta.features gets filled in with Default::default values for other cache statuses. So we only want to filter those for which we actually downloaded but do not match the requirements.

flub · 2020-11-03T14:46:45Z

src/actors/common/cache.rs

+        let future = request
+            .compute(temp_file.path())
+            .and_then(move |status: CacheStatus| {
+                if let Some(ref cache_path) = cache_path {
+                    sentry::configure_scope(|scope| {
+                        scope.set_extra(
+                            &format!("cache.{}.cache_path", name),
+                            cache_path.to_string_lossy().into(),
+                        );
+                    });
+
+                    log::trace!("Creating {} at path {:?}", name, cache_path);
+                }

-                log::trace!("Creating {} at path {:?}", name, cache_path);
-            }
+                let byteview = ByteView::open(temp_file.path())?;

-            let byteview = ByteView::open(temp_file.path())?;
+                metric!(
+                    counter(&format!("caches.{}.file.write", name)) += 1,
+                    "status" => status.as_ref(),
+                );
+                metric!(
+                    time_raw(&format!("caches.{}.file.size", name)) = byteview.len() as u64,
+                    "hit" => "false"
+                );

-            metric!(
-                counter(&format!("caches.{}.file.write", name)) += 1,
-                "status" => status.as_ref(),
-            );
-            metric!(
-                time_raw(&format!("caches.{}.file.size", name)) = byteview.len() as u64,
-                "hit" => "false"
-            );
+                let path = match cache_path {
+                    Some(ref cache_path) => {
+                        status.persist_item(cache_path, temp_file)?;
+                        CachePath::Cached(cache_path.to_path_buf())
+                    }
+                    None => CachePath::Temp(temp_file.into_temp_path()),
+                };

-            let path = match cache_path {
-                Some(ref cache_path) => {
-                    status.persist_item(cache_path, temp_file)?;
-                    CachePath::Cached(cache_path.to_path_buf())
-                }
-                None => CachePath::Temp(temp_file.into_temp_path()),
-            };
-
-            Ok(request.load(key.scope.clone(), status, byteview, path))
-        });
+                Ok(request.load(key.scope.clone(), status, byteview, path))
+            });


This code didn't change, I only added the type signature to the |status: CacheStatus| closure and the rest is rust-fmt's doing.

flub · 2020-11-03T15:05:20Z

src/actors/objects/mod.rs

+                .filter(|response| match response {
+                    // Make sure we only return objects which provide the requested info
+                    Ok(object_meta) => {
+                        if object_meta.status == CacheStatus::Positive {
+                            // object_meta.features is meaningless when CacheStatus != Positive
+                            match purpose {
+                                ObjectPurpose::Unwind => object_meta.features.has_unwind_info,
+                                ObjectPurpose::Debug => {
+                                    object_meta.features.has_debug_info
+                                        || object_meta.features.has_symbols
+                                }
+                                ObjectPurpose::Source => object_meta.features.has_sources,
+                            }
+                        } else {
+                            true
+                        }
+                    }
+                    Err(_) => true,


This .filter() is the actual bugfix. The the minidump processor assumes that when it finds a file in the CFI cache for the module it has a file with valid cfi info. In turn the file gets into the cfi cache because the cfi actor assumes that the object actor returns a file fit for purpose, and it asked for a CFI file. However the object actor's ranking mechanism didn't respect that. Adding this makes it respect this.

flub · 2020-11-03T15:18:32Z

src/actors/objects/mod.rs

+                            None => {
+                                if archive.objects().all(|r| r.is_err()) {
+                                    return Ok(CacheStatus::Malformed);
+                                } else {
+                                    return Ok(CacheStatus::Negative);
+                                }
+                            }


This fixes a bug where if an archive contained only malformed objects it would show up as missing rather than malformed. Arguably this isn't aggressive enough and should return malformed if the object was not found and any member of the archive failed to be parsed.

this would be good to write in a code comment

src/actors/common/cache.rs

Swatinem · 2020-11-04T09:47:51Z

src/actors/common/cache.rs

-                });
+        let future = request
+            .compute(temp_file.path())
+            .and_then(move |status: CacheStatus| {


"hide whitespace changes" is your friend ;-) I wonder why you need the explicit type declaration here though

This is entirely a subjective readability choice. I'd say this is no different than spelling out the types in functions, and this is a large enough function...

Swatinem · 2020-11-04T09:57:34Z

src/actors/objects/mod.rs

+                            None => {
+                                if archive.objects().all(|r| r.is_err()) {
+                                    return Ok(CacheStatus::Malformed);
+                                } else {
+                                    return Ok(CacheStatus::Negative);
+                                }
+                            }


this would be good to write in a code comment

src/actors/objects/mod.rs

Swatinem · 2020-11-04T10:11:12Z

src/actors/objects/mod.rs

+                            true
+                        }
+                    }
+                    Err(_) => true,


just out of curiosity: the new filter now throws away things we can’t use, but why does it pass through errors and negative cache statuses?

because all those could have been object files which might have contained the info we needed. but we don't know until we can actually fetch it. and passing them through allows us to report on their status later (download error, malformed, negative cache). this whole behaviour of only returning one result here a bit questionable and may have to change to improve reporting

Co-authored-by: Arpad Borsos <arpad.borsos@sentry.io>

Only just realised there's also a "batch" button. oh well Co-authored-by: Arpad Borsos <arpad.borsos@sentry.io>

untitaker · 2020-11-10T10:32:12Z

src/actors/objects/mod.rs

                        Err(e) => {
                            log::debug!("Failed to download: {:#?}", e);
-                            return (3, *i);


iirc we did this for stable min such that ties are resolved by order of sources.

The i here entirely depends on the order of the futures being executed above above calling download_svc.list_files(). Practically this means there is no order, it's a race on who gets executed by the executor first (for non-sentry sources) or how fast the network is (for the sentry source).

At least that's my understanding and the reason I took it out. I don't think it enforces anything and only makes the code look more complicated.

join_all preserves order of futures. list_files can return any order it wants, but joining all list_files calls together resembles the source order.

In theory this gives you the possibility to upload your own Windows kernel symbols and let them have precedence over our own built-in symbol source. I am not sure if anybody relies on this.

This is definitely behavior we should retain.

untitaker · 2020-11-10T10:34:11Z

src/actors/objects/mod.rs

+                    }
+                })
+                .filter(|response| match response {
+                    // Make sure we only return objects which provide the requested info


Can we dedupe this with the content in min_by_key? iiuc all scores of 2 should basically be filtered out.

Perhaps the closure of min_by_key should go into a filter_map before min_by happens. Or we refactor this entire thing into a regular for-loop.

Thanks for complaining about this. I've looked at all the consumers again and concluded the filtering needs to be moved to before the min_by_key in order to still return a possible Err if we filtered out an object file.

I'm not sure I would like to merge the two, I think having the two as separate operations is easier to understand as each have a defined scope.

Yeah no worries was just an idea.

If we didnt find the object in an archive but it was meant to be there while at the same time there was a malformed file, it is safer to assume that the malformed file was the one we needed rather than treat it as missing.

Because the whole find function returns an Option<Result<ObjectFileMeta, _>> we should fiter before we find the most suitable object. This way when we filtered out an object the selection could still return a relevant Err. Filtering after does not allow this anymore.

Floris Bruynooghe added 4 commits October 29, 2020 18:36

More clarifications

1217932

Allow malformed objects in archives

5987169

If there's an archive, but the file inside is malformed it was shown as simply missing. This fixes this to still give a malformed marker.

Only filter for positive caches

7f824e5

object_meta.features gets filled in with Default::default values for other cache statuses. So we only want to filter those for which we actually downloaded but do not match the requirements.

flub commented Nov 3, 2020

View reviewed changes

Add a changelog

8053e6f

flub marked this pull request as ready for review November 3, 2020 15:22

flub requested a review from a team November 3, 2020 15:22

flub mentioned this pull request Nov 3, 2020

fix(cfi): Treat no CFI as missing CFI #280

Closed

Swatinem approved these changes Nov 4, 2020

View reviewed changes

Floris Bruynooghe and others added 3 commits November 4, 2020 11:14

use intra-doc link

905cd8c

Co-authored-by: Arpad Borsos <arpad.borsos@sentry.io>

typo

06a0dfe

Co-authored-by: Arpad Borsos <arpad.borsos@sentry.io>

typos

4a37f4b

Only just realised there's also a "batch" button. oh well Co-authored-by: Arpad Borsos <arpad.borsos@sentry.io>

jan-auer requested review from untitaker and jan-auer November 10, 2020 10:26

untitaker approved these changes Nov 10, 2020

View reviewed changes

Floris Bruynooghe added 3 commits November 11, 2020 17:25

Mark malformed a little more eager in archives

a1e6f1c

If we didnt find the object in an archive but it was meant to be there while at the same time there was a malformed file, it is safer to assume that the malformed file was the one we needed rather than treat it as missing.

Preserve the order or sources

e8a98ed

flub requested a review from untitaker November 12, 2020 11:42

flub merged commit 3e4e534 into master Nov 12, 2020

flub deleted the fix/bad-unwind-status branch November 12, 2020 13:13

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fix(objects): Make sure returned files can be used for purpose #279

fix(objects): Make sure returned files can be used for purpose #279

flub commented Oct 29, 2020

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Swatinem Nov 4, 2020

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untitaker Nov 10, 2020 •

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untitaker Nov 12, 2020

fix(objects): Make sure returned files can be used for purpose #279

fix(objects): Make sure returned files can be used for purpose #279

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flub commented Oct 29, 2020

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untitaker Nov 10, 2020 • edited Loading

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