[Git][ghc/ghc][wip/T13660] base: Ensure that POSIX FilePaths don't contain NULs

[Ben Gamari (@bgamari)]

Ben Gamari pushed to branch wip/T13660 at Glasgow Haskell Compiler / GHC


Commits:
95a3e3a2 by Ben Gamari at 2023-03-26T09:27:23-04:00
base: Ensure that POSIX FilePaths don't contain NULs

POSIX filepaths may not contain the NUL octet but previously we did not
reject such paths. This could be exploited by untrusted input to cause
discrepancies between various `FilePath` queries and the opened
filename. For instance, `readFile "hello.so\x00.txt"` would open the
file `"hello.so"` yet `takeFileExtension` would return `".txt"`.

Fixes #13660.

- - - - -


1 changed file:

- libraries/base/System/Posix/Internals.hs


Changes:

=====================================
libraries/base/System/Posix/Internals.hs
=====================================
@@ -164,13 +164,22 @@ fdGetMode fd = do
 
 #if defined(mingw32_HOST_OS)
 withFilePath :: FilePath -> (CWString -> IO a) -> IO a
-withFilePath = withCWString
+withFilePath fp f = do
+    checkForInteriorNuls fp
+    withCWString fp f
 
 newFilePath :: FilePath -> IO CWString
-newFilePath = newCWString
+newFilePath fp = do
+    checkForInteriorNuls fp
+    newCWString fp
 
 peekFilePath :: CWString -> IO FilePath
 peekFilePath = peekCWString
+
+-- | Check a 'FilePath' for internal NUL codepoints as these are
+-- disallowed in Windows filepaths. See #13660.
+checkForInteriorNuls :: FilePath -> IO ()
+checkForInteriorNuls s = when ('\0' `elem` s) throwInternalNulError
 #else
 
 withFilePath :: FilePath -> (CString -> IO a) -> IO a
@@ -178,13 +187,41 @@ newFilePath :: FilePath -> IO CString
 peekFilePath :: CString -> IO FilePath
 peekFilePathLen :: CStringLen -> IO FilePath
 
-withFilePath fp f = getFileSystemEncoding >>= \enc -> GHC.withCString enc fp f
-newFilePath fp = getFileSystemEncoding >>= \enc -> GHC.newCString enc fp
+withFilePath fp f = do
+    enc <- getFileSystemEncoding
+    GHC.withCStringLen enc fp $ \(str, len) -> do
+        checkForInteriorNuls fp (str, len)
+        f str
+newFilePath fp = do
+    enc <- getFileSystemEncoding
+    (str, len) <- GHC.newCStringLen enc fp
+    checkForInteriorNuls fp (str, len)
+    return str
 peekFilePath fp = getFileSystemEncoding >>= \enc -> GHC.peekCString enc fp
 peekFilePathLen fp = getFileSystemEncoding >>= \enc -> GHC.peekCStringLen enc fp
 
+-- | Check an encoded 'FilePath' for internal NUL octets as these are
+-- disallowed in POSIX filepaths. See #13660.
+checkForInteriorNuls :: FilePath -> CStringLen -> IO ()
+checkForInteriorNuls fp (str, len) =
+    when (cstringLen# str /= len) throwInternlNulError
+    -- N.B. If the string contains internal NUL codeunits then the strlen will
+    -- indicate a size smaller than that returned by withCStringLen.
 #endif
 
+throwInternalNulError :: IOError
+throwInternalNulError = ioError err
+  where
+    err =
+      IOError
+        { ioe_handle = Nothing
+        , ioe_type = InvalidArgument
+        , ioe_location = "checkForInteriorNuls"
+        , ioe_description = "FilePaths must not contain internal NUL code units."
+        , ioe_errno = Nothing
+        , ioe_filename = Just fp
+        }
+
 -- ---------------------------------------------------------------------------
 -- Terminal-related stuff
 



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/95a3e3a2738f0a75e373652a9e524693d4e3cd6f

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/95a3e3a2738f0a75e373652a9e524693d4e3cd6f
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