fix: broken pgm having memory access error

Fixes 4552
Caught during fuzzing with address sanitizer.

The source of the problem was a corrupted/truncated pgm file. Several
minor modifications in this PR shore up various cascading errors that
followed. Not all were directly causal to the sanitizer trigger, in
some cases I fixed what appeared to be related areas.

* In imagebuf.cpp, any time we free the local pixel memory m_pixels,
  also explicitly clear the m_bufspan that has a span representation
  of the usable memory and its bounds.
* An extra check related to oiiotool --printstats to make sure that the
  image is valid before passing along to stats collection.
* In pnminput.cpp, a better error message when we hit a premature end
  of file.

With these fixes in place, we seem to get a graceful error message and
exit when running the POC that was provided with the bug report.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

src/libOpenImageIO/imagebuf.cpp

@@ -687,6 +687,7 @@ ImageBufImpl::new_pixels(size_t size, const void* data)
         // consider this an uninitialized ImageBuf, issue an error, and hope
         // it's handled well downstream.
         m_pixels.reset();
+        m_bufspan = make_span<std::byte>(nullptr, 0);
         OIIO::debugfmt("ImageBuf unable to allocate {} bytes ({})\n", size,
                        e.what());
         error("ImageBuf unable to allocate {} bytes ({})\n", size, e.what());
@@ -720,6 +721,8 @@ ImageBufImpl::free_pixels()
         m_allocated_size = 0;
     }
     m_pixels.reset();
+    // print("IB Freed pixels of length {}\n", m_bufspan.size());
+    m_bufspan = make_span<std::byte>(nullptr, 0);
     m_deepdata.free();
     m_storage = ImageBuf::UNINITIALIZED;
     m_blackpixel.clear();
@@ -806,6 +809,7 @@ ImageBufImpl::clear()
     m_spec             = ImageSpec();
     m_nativespec       = ImageSpec();
     m_pixels.reset();
+    m_bufspan        = make_span<std::byte>(nullptr, 0);
     m_localpixels    = nullptr;
     m_spec_valid     = false;
     m_pixels_valid   = false;

src/oiiotool/oiiotool.cpp

@@ -5801,7 +5801,8 @@ action_printstats(Oiiotool& ot, cspan<const char*> argv)
     auto options      = ot.extract_options(command);
     bool allsubimages = options.get_int("allsubimages", ot.allsubimages);
 
-    ot.read();
+    if (!ot.read())
+        return;
     ImageRecRef top = ot.top();
 
     print_info_options opt = ot.info_opts();
@@ -5818,6 +5819,7 @@ action_printstats(Oiiotool& ot, cspan<const char*> argv)
                       opt.roi.chend);
     }
     std::string errstring;
+    OIIO_ASSERT(top.get());
     print_info(std::cout, ot, top.get(), opt, errstring);
 
     ot.printed_info = true;

src/pnm.imageio/pnminput.cpp

@@ -223,8 +223,10 @@ PNMInput::read_file_scanline(void* data, int y)
                 numbytes = m_spec.nchannels * 4 * m_spec.width;
             else
                 numbytes = m_spec.scanline_bytes();
-            if (size_t(numbytes) > m_remaining.size())
+            if (size_t(numbytes) > m_remaining.size()) {
+                errorfmt("Premature end of file");
                 return false;
+            }
             buf.assign(m_remaining.begin(), m_remaining.begin() + numbytes);
 
             m_remaining.remove_prefix(numbytes);

testsuite/pnm/ref/out.txt

@@ -69,3 +69,14 @@ Reading ../oiio-images/pnm/test-3.pfm
     oiio:ColorSpace: "Rec709"
     pnm:bigendian: 1
     pnm:binary: 1
+Reading src/bad-4552.pgm
+oiiotool ERROR: -info : SHA-1: Premature end of file
+Full command line was:
+> oiiotool --info -v -a --hash --printstats src/bad-4552.pgm
+src/bad-4552.pgm     :    9 x    1, 1 channel, uint8 pnm
+    channel list: Y
+    oiio:ColorSpace: "Rec709"
+    pnm:binary: 1
+oiiotool ERROR: read : "src/bad-4552.pgm": Premature end of file
+Full command line was:
+> oiiotool --info -v -a --hash --printstats src/bad-4552.pgm

testsuite/pnm/run.py

@@ -4,6 +4,8 @@
 # SPDX-License-Identifier: Apache-2.0
 # https://github.com/AcademySoftwareFoundation/OpenImageIO
 
+redirect = ' >> out.txt 2>&1 '
+
 imagedir = OIIO_TESTSUITE_IMAGEDIR + "/pnm"
 
 for f in [ "bw-ascii.pbm", "bw-binary.pbm",
@@ -16,3 +18,8 @@
 for f in files:
     command += info_command (imagedir + "/" + f,
                              safematch=True, hash=True)
+
+# Damaged files
+files = [ "src/bad-4552.pgm" ]
+for f in files:
+    command += info_command (f, extraargs="--printstats", failureok=True)

testsuite/pnm/src/bad-4552.pgm

@@ -0,0 +1,4 @@
+P5
+9 1
+255
+�