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authornobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2015-02-02 01:51:37 +0000
committernobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>2015-02-02 01:51:37 +0000
commit92c1538d48f79cb8d7645d29ff7ecdc51ebd30ab (patch)
treed40aa92be7efe7e97722f891ef421ff3acb5bd56 /doc
parent5146f5abe9adaf7760728ec279e69e021a234723 (diff)
security.rdoc: update about Symbol GC [ci skip]
* doc/security.rdoc (Symbols): update about Symbol GC. Symbols explicitly converted from Strings now can be collected, but reflection/metaprogramming still can cause memory flooding. [Fix GH-725] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49468 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Diffstat (limited to 'doc')
-rw-r--r--doc/security.rdoc22
1 files changed, 9 insertions, 13 deletions
diff --git a/doc/security.rdoc b/doc/security.rdoc
index d8efca0..ff2da46 100644
--- a/doc/security.rdoc
+++ b/doc/security.rdoc
@@ -66,20 +66,16 @@ method, variable and constant names. The reason for this is that symbols are
simply integers with names attached to them, so they are faster to look up in
hashtables.
-Once a symbol is created, the memory used by it is never freed. If you convert
-user input to symbols with +to_sym+ or +intern+, it is possible for an attacker
-to mount a denial of service attack against your application by flooding it
-with unique strings. Because each string is kept in memory until the Ruby
-process exits, this will cause memory consumption to grow and grow until Ruby
-runs out of memory and crashes.
-
Be careful with passing user input to methods such as +send+,
-+instance_variable_get+ or +_set+, +const_get+ or +_set+, etc. as these methods
-will convert string parameters to symbols internally and pose the same DoS
-potential as direct conversion through +to_sym+/+intern+.
-
-The workaround to this is simple - don't convert user input to symbols. You
-should attempt to leave user input in string form instead.
++instance_variable_get+ or +_set+, +const_get+ or +_set+, etc.
+as these methods will convert string parameters to immortal symbols internally.
+This means that the memory used by the symbols are never freed. This could
+allow a user to mount a denial of service attack against your application by
+flooding it with unique strings, which will cause memory to grow indefinitely
+until the Ruby process is killed or causes the system to slow to a halt.
+
+The workaround to this is simple - don't call reflection/metaprogramming
+methods with user input.
== Regular expressions