[PATCH] Linux: Adjust gedents64 buffer size to int range [BZ #24740]

[Florian Weimer <fweimer at redhat dot com>]

The kernel interface uses type unsigned int, but there is an
internal conversion to int, so INT_MAX is the correct limit.
Part of the buffer will always be unused, but this is not a
problem.  Such huge buffers do not occur in practice anyway.

2019-06-27  Florian Weimer  <fweimer@redhat.com>

	[BZ #24740]
	* sysdeps/unix/sysv/linux/getdents64.c (__getdents64): Adjust
	buffer size if necessary.
	* sysdeps/unix/sysv/linux/mips/mips64/getdents64.c (__getdents64):
	Likewise.
	* sysdeps/unix/sysv/linux/tst-getdents64.c (large_buffer_check):
	New function.
	(large_buffer_checks): Likewise.
	(do_test): Call large_buffer_checks.

diff --git a/sysdeps/unix/sysv/linux/getdents64.c b/sysdeps/unix/sysv/linux/getdents64.c
index a6dd22106d..5e3ef9994e 100644
--- a/sysdeps/unix/sysv/linux/getdents64.c
+++ b/sysdeps/unix/sysv/linux/getdents64.c
@@ -19,11 +19,16 @@
 #include <string.h>
 #include <dirent.h>
 #include <errno.h>
+#include <limits.h>
 
 /* The kernel struct linux_dirent64 matches the 'struct dirent64' type.  */
 ssize_t
 __getdents64 (int fd, void *buf, size_t nbytes)
 {
+  /* The system call takes an unsigned int argument, and some length
+     checks in the kernel use an int type.  */
+  if (nbytes > INT_MAX)
+    nbytes = INT_MAX;
   return INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
 }
 libc_hidden_def (__getdents64)
diff --git a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
index 1e22fa4325..8bf3abb0e0 100644
--- a/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
+++ b/sysdeps/unix/sysv/linux/mips/mips64/getdents64.c
@@ -23,12 +23,18 @@
 #include <sys/param.h>
 #include <unistd.h>
 #include <scratch_buffer.h>
+#include <limits.h>
 
 ssize_t
 __getdents64 (int fd, void *buf0, size_t nbytes)
 {
   char *buf = buf0;
 
+  /* The system call takes an unsigned int argument, and some length
+     checks in the kernel use an int type.  */
+  if (nbytes > INT_MAX)
+    nbytes = INT_MAX;
+
 #ifdef __NR_getdents64
   ssize_t ret = INLINE_SYSCALL_CALL (getdents64, fd, buf, nbytes);
   if (ret != -1)
diff --git a/sysdeps/unix/sysv/linux/tst-getdents64.c b/sysdeps/unix/sysv/linux/tst-getdents64.c
index c1f7721221..ece46123f3 100644
--- a/sysdeps/unix/sysv/linux/tst-getdents64.c
+++ b/sysdeps/unix/sysv/linux/tst-getdents64.c
@@ -19,6 +19,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <limits.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -28,6 +29,48 @@
 #include <support/xunistd.h>
 #include <unistd.h>
 
+/* Called by large_buffer_checks below.  */
+static void
+large_buffer_check (int fd, char *large_buffer, size_t large_buffer_size)
+{
+  xlseek (fd, 0, SEEK_SET);
+  ssize_t ret = getdents64 (fd, large_buffer, large_buffer_size);
+  if (ret < 0)
+    FAIL_EXIT1 ("getdents64 for buffer of %zu bytes failed: %m",
+                large_buffer_size);
+  if (ret < offsetof (struct dirent64, d_name))
+    FAIL_EXIT1 ("getdents64 for buffer of %zu returned small value %zd",
+                large_buffer_size, ret);
+}
+
+/* Bug 24740: Make sure that the system call argument is adjusted
+   properly for the int type.  A large value should stay a large
+   value, and not wrap around to something small, causing the system
+   call to fail with EINVAL.  */
+static void
+large_buffer_checks (int fd)
+{
+  size_t large_buffer_size = UINT_MAX;
+  large_buffer_size += 2;
+  if (large_buffer_size > 2)
+    {
+      char *large_buffer = malloc (large_buffer_size);
+      if (large_buffer == NULL)
+        printf ("warning: could not allocate %zu bytes of memory,"
+                " subtests skipped\n", large_buffer_size);
+      else
+        {
+          large_buffer_check (fd, large_buffer, INT_MAX);
+          large_buffer_check (fd, large_buffer, (size_t) INT_MAX + 1);
+          large_buffer_check (fd, large_buffer, (size_t) INT_MAX + 2);
+          large_buffer_check (fd, large_buffer, UINT_MAX);
+          large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 1);
+          large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 2);
+        }
+      free (large_buffer);
+    }
+}
+
 static int
 do_test (void)
 {
@@ -105,6 +148,8 @@ do_test (void)
       rewinddir (reference);
     }
 
+  large_buffer_checks (fd);
+
   xclose (fd);
   closedir (reference);
   return 0;