linux-kernel - [PATCH v2 3/6] elf: Fix failure handling in _dl_map_object_from

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Message-Id: <8ebf571196dd499c61983dbf53c94c68ebd458cc.1606319495.git.szabolcs.nagy@arm.com>
Date:   Fri, 27 Nov 2020 13:20:29 +0000
From:   Szabolcs Nagy <szabolcs.nagy@....com>
To:     libc-alpha@...rceware.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>,
        Mark Brown <broonie@...nel.org>,
        kernel-hardening@...ts.openwall.com,
        Topi Miettinen <toiwoton@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v2 3/6] elf: Fix failure handling in _dl_map_object_from_fd

There are many failure paths that call lose to do local cleanups
in _dl_map_object_from_fd, but it did not clean everything.

Handle l_phdr, l_libname and mapped segments in the common failure
handling code.

There are various bits that may not be cleaned properly on failure
(e.g. executable stack, tlsid, incomplete dl_map_segments).
---
 elf/dl-load.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 21e55deb19..9c71b7562c 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -914,8 +914,15 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
   /* The file might already be closed.  */
   if (fd != -1)
     (void) __close_nocancel (fd);
+  if (l != NULL && l->l_map_start != 0)
+    _dl_unmap_segments (l);
   if (l != NULL && l->l_origin != (char *) -1l)
     free ((char *) l->l_origin);
+  if (l != NULL && !l->l_libname->dont_free)
+    free (l->l_libname);
+  if (l != NULL && l->l_phdr_allocated)
+    free ((void *) l->l_phdr);
+
   free (l);
   free (realname);
 
@@ -1256,7 +1263,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
     errstring = _dl_map_segments (l, fd, header, type, loadcmds, nloadcmds,
 				  maplength, has_holes, loader);
     if (__glibc_unlikely (errstring != NULL))
-      goto call_lose;
+      {
+	/* Mappings can be in an inconsistent state: avoid unmap.  */
+	l->l_map_start = l->l_map_end = 0;
+	goto call_lose;
+      }
 
     /* Process program headers again after load segments are mapped in
        case processing requires accessing those segments.  Scan program
@@ -1294,14 +1305,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
       || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
 	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
     {
-      /* We are not supposed to load this object.  Free all resources.  */
-      _dl_unmap_segments (l);
-
-      if (!l->l_libname->dont_free)
-	free (l->l_libname);
-
-      if (l->l_phdr_allocated)
-	free ((void *) l->l_phdr);
 
       if (l->l_flags_1 & DF_1_PIE)
 	errstring
@@ -1392,6 +1395,9 @@ cannot enable executable stack as shared object requires");
   /* Signal that we closed the file.  */
   fd = -1;
 
+  /* Failures before this point are handled locally via lose.
+     No more failures are allowed in this function until return.  */
+
   /* If this is ET_EXEC, we should have loaded it as lt_executable.  */
   assert (type != ET_EXEC || l->l_type == lt_executable);
 
-- 
2.17.1