Handle ENAMETOOLONG on Linux (#1940) (#1955)

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 #1940).

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

4 files changed, 48 insertions, 1 deletions

diff --git a/CREDITS b/CREDITS
index 280c3b1c..cc7e7a59 100644
--- a/CREDITS
+++ b/CREDITS
@@ -745,6 +745,10 @@ N: David Knaack
 W: https://github.com/davidkna
 I: 1921
 
+N: Nikita Radchenko
+W: https://github.com/nradchenko
+I: 1940
+
 N: MaWe2019
 W: https://github.com/MaWe2019
 I: 1953
@@ -761,4 +765,4 @@ I: 1598
 
 N: Xuehai Pan
 W: https://github.com/XuehaiPan
-I: 1948
+I: 1948
\ No newline at end of file
diff --git a/HISTORY.rst b/HISTORY.rst
index a8284ad2..ccc5c829 100644
--- a/HISTORY.rst
+++ b/HISTORY.rst
@@ -34,6 +34,8 @@ XXXX-XX-XX
 - 1913_: [Linux] wait_procs seemingly ignoring timeout, TimeoutExpired thrown
 - 1919_: [Linux] sensors_battery() can raise TypeError on PureOS.
 - 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
 - 1948_: Process' memoize_when_activated decorator was not thread-safe.  (patch
   by Xuehai Pan)
 - 1953_: [Windows] disk_partitions() crashes due to insufficient buffer len.
diff --git a/psutil/_pslinux.py b/psutil/_pslinux.py
index 3afe6c65..1917e20d 100644
--- a/psutil/_pslinux.py
+++ b/psutil/_pslinux.py
@@ -832,6 +832,9 @@ class Connections:
                 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:['):
@@ -2101,6 +2104,9 @@ class Process(object):
                 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
diff --git a/psutil/tests/test_linux.py b/psutil/tests/test_linux.py
index 23f6b221..3fda7874 100755
--- a/psutil/tests/test_linux.py
+++ b/psutil/tests/test_linux.py
@@ -1446,6 +1446,25 @@ class TestMisc(PsutilTestCase):
             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
@@ -1830,6 +1849,22 @@ class TestProcess(PsutilTestCase):
                 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):