changeset 40626:87a872555e90

revlog: detect incomplete revlog reads _readsegment() is supposed to return N bytes of revlog revision data starting at a file offset. Surprisingly, its behavior before this patch never verified that it actually read and returned N bytes! Instead, it would perform the read(), then return whatever data was available. And even more surprisingly, nothing in the call chain appears to have been validating that it received all the data it was expecting. This behavior could lead to partial or incomplete revision chunks being operated on. This could result in e.g. cached deltas being applied against incomplete base revisions. The delta application process would happily perform this operation. Only hash verification would detect the corruption and save us. This commit changes the behavior of raw revlog reading to validate that we actually read() the number of bytes that were requested. We will raise a more specific error faster, rather than possibly have it go undetected or manifest later in the call stack, at delta application or hash verification. Differential Revision: https://phab.mercurial-scm.org/D5266
author Gregory Szorc <gregory.szorc@gmail.com>
date Tue, 13 Nov 2018 12:30:59 -0800
parents 39369475445c
children e9293c5f8bb9
files mercurial/revlog.py
diffstat 1 files changed, 20 insertions(+), 1 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/revlog.py	Tue Oct 30 16:50:05 2018 -0700
+++ b/mercurial/revlog.py	Tue Nov 13 12:30:59 2018 -0800
@@ -1342,6 +1342,8 @@
         original seek position will NOT be restored.
 
         Returns a str or buffer of raw byte data.
+
+        Raises if the requested number of bytes could not be read.
         """
         # Cache data both forward and backward around the requested
         # data, in a fixed size window. This helps speed up operations
@@ -1353,9 +1355,26 @@
         with self._datareadfp(df) as df:
             df.seek(realoffset)
             d = df.read(reallength)
+
         self._cachesegment(realoffset, d)
         if offset != realoffset or reallength != length:
-            return util.buffer(d, offset - realoffset, length)
+            startoffset = offset - realoffset
+            if len(d) - startoffset < length:
+                raise error.RevlogError(
+                    _('partial read of revlog %s; expected %d bytes from '
+                      'offset %d, got %d') %
+                    (self.indexfile if self._inline else self.datafile,
+                     length, realoffset, len(d) - startoffset))
+
+            return util.buffer(d, startoffset, length)
+
+        if len(d) < length:
+            raise error.RevlogError(
+                _('partial read of revlog %s; expected %d bytes from offset '
+                  '%d, got %d') %
+                (self.indexfile if self._inline else self.datafile,
+                 length, offset, len(d)))
+
         return d
 
     def _getsegment(self, offset, length, df=None):