Handle ENAMETOOLONG when resolving fd symlinks in procfs on Linux (gi…

…ampaolo#1940)

When resolving process file descriptors symlinks in procfs (/proc/PID/fd/FD),
the kernel can only deal with file paths no longer than PAGE_SIZE
(which usually equals to PATH_MAX).

https://elixir.bootlin.com/linux/v5.12/source/fs/proc/base.c#L1759

Resolving fd symlink that corresponds to a file with a path longer
than PATH_MAX with readlink(2) would result in ENAMETOOLONG error
(see details in giampaolo#1940).

We can do nothing to fix this in userspace; therefore these errors
should be ignored.

CREDITS

@@ -744,3 +744,7 @@ I: 1913
 N: David Knaack
 W: https://github.com/davidkna
 I: 1921
+
+N: Nikita Radchenko
+W: https://github.com/nradchenko
+I: 1940

HISTORY.rst

@@ -23,6 +23,8 @@ XXXX-XX-XX
 - 1874_: [Solaris] swap output error due to incorrect range.
 - 1913_: [Linux] wait_procs seemingly ignoring timeout, TimeoutExpired thrown
 - 1921_: [Windows] psutil.swap_memory() shows committed memory instead of swap
+- 1940_: [Linux] psutil does not handle ENAMETOOLONG when accessing process
+  file descriptors in procfs
 
 5.8.0
 =====

psutil/_pslinux.py

@@ -832,6 +832,9 @@ def get_proc_inodes(self, pid):
                 if err.errno == errno.EINVAL:
                     # not a link
                     continue
+                if err.errno == errno.ENAMETOOLONG:
+                    # file name too long
+                    continue
                 raise
             else:
                 if inode.startswith('socket:['):
@@ -2098,6 +2101,9 @@ def open_files(self):
                 if err.errno == errno.EINVAL:
                     # not a link
                     continue
+                if err.errno == errno.ENAMETOOLONG:
+                    # file name too long
+                    continue
                 raise
             else:
                 # If path is not an absolute there's no way to tell

psutil/tests/test_linux.py

@@ -1450,6 +1450,25 @@ def test_pid_exists_no_proc_status(self):
             assert psutil.pid_exists(os.getpid())
             assert m.called
 
+    def test_get_proc_inodes_fd_broken(self):
+        # Simulate a case where /proc/{pid}/fd/{fd} symlink
+        # points to a file with full path longer than PATH_MAX
+
+        def get_inodes():
+            connections = psutil._pslinux.Connections()
+            connections._procfs_path = psutil._common.get_procfs_path()
+            return connections.get_proc_inodes(os.getpid())
+
+        p = psutil.Process()
+        files = p.open_files()
+        with open(self.get_testfn(), 'w'):
+            # give the kernel some time to see the new file
+            call_until(p.open_files, "len(ret) != %i" % len(files))
+            patch_point = 'psutil._pslinux.os.readlink'
+            with mock.patch(patch_point,
+                            side_effect=OSError(errno.ENAMETOOLONG, "")) as m:
+                assert not get_inodes()
+                assert m.called
 
 # =====================================================================
 # --- sensors
@@ -1834,6 +1853,22 @@ def test_open_files_fd_gone(self):
                 assert not files
                 assert m.called
 
+    def test_open_files_fd_broken(self):
+        # Simulate a case where /proc/{pid}/fd/{fd} symlink
+        # points to a file with full path longer than PATH_MAX
+
+        p = psutil.Process()
+        files = p.open_files()
+        with open(self.get_testfn(), 'w'):
+            # give the kernel some time to see the new file
+            call_until(p.open_files, "len(ret) != %i" % len(files))
+            patch_point = 'psutil._pslinux.os.readlink'
+            with mock.patch(patch_point,
+                            side_effect=OSError(errno.ENAMETOOLONG, "")) as m:
+                files = p.open_files()
+                assert not files
+                assert m.called
+
     # --- mocked tests
 
     def test_terminal_mocked(self):