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

[Ben Gamari (@bgamari)]

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


Commits:
2c965958 by Ben Gamari at 2023-03-10T11:32:40-05:00
base: Ensure that FilePaths don't contain NULs on POSIX

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
=====================================
@@ -178,11 +178,43 @@ 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) = go (len-2)
+  where
+    -- here we ensure that the body of the string (that is, excluding the terminal
+    -- NUL) contains no NUL octets.
+    go i | i < 0 = return ()
+    go i = do
+      c <- peekByteOff str i :: IO Word8
+      when (c == 0) $ do
+        ioError err
+      go (i-1)
+
+    err =
+        IOError
+          { ioe_handle = Nothing
+          , ioe_type = InvalidArgument
+          , ioe_location = "checkForInteriorNuls"
+          , ioe_description = "POSIX filepaths must not contain internal NUL octets."
+          , ioe_errno = Nothing
+          , ioe_filename = Just fp
+          }
+
 #endif
 
 -- ---------------------------------------------------------------------------



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/2c9659587b022e6bfdcc89afcb316ee666673280

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/2c9659587b022e6bfdcc89afcb316ee666673280
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