2005-09-09 Roland McGrath <[email protected]>

	* elf_update.c (write_file): Stat the file and fchmod it after update
	if its mode had S_ISUID or S_ISGID bits set.

2 files changed, 26 insertions, 0 deletions

diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index bd710aee..35667cee 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,3 +1,8 @@
+2005-09-09  Roland McGrath  <[email protected]>
+
+	* elf_update.c (write_file): Stat the file and fchmod it after update
+	if its mode had S_ISUID or S_ISGID bits set.
+
 2005-08-28  Ulrich Drepper  <[email protected]>
 
 	* elf32_getphdr.c: Include <system.h>.  Use pread_retry instead of
diff --git a/libelf/elf_update.c b/libelf/elf_update.c
index 5d6c6b7a..f380e2b9 100644
--- a/libelf/elf_update.c
+++ b/libelf/elf_update.c
@@ -22,6 +22,7 @@
 #include <libelf.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <sys/stat.h>
 
 #include "libelfP.h"
 
@@ -31,6 +32,14 @@ write_file (Elf *elf, off_t size, int change_bo, size_t shnum)
 {
   int class = elf->class;
 
+  /* Check the mode bits now, before modification might change them.  */
+  struct stat st;
+  if (unlikely (fstat (elf->fildes, &st) != 0))
+    {
+      __libelf_seterrno (ELF_E_WRITE_ERROR);
+      return -1;
+    }
+
   /* Adjust the size in any case.  We do this even if we use `write'.
      We cannot do this if this file is in an archive.  We also don't
      do it *now* if we are shortening the file since this would
@@ -87,6 +96,18 @@ write_file (Elf *elf, off_t size, int change_bo, size_t shnum)
       size = -1;
     }
 
+  /* POSIX says that ftruncate and write may clear the S_ISUID and S_ISGID
+     mode bits.  So make sure we restore them afterwards if they were set.
+     This is not atomic if someone else chmod's the file while we operate.  */
+  if (size != -1
+      && unlikely (st.st_mode & (S_ISUID | S_ISGID))
+      /* fchmod ignores the bits we cannot change.  */
+      && unlikely (fchmod (elf->fildes, st.st_mode) != 0))
+    {
+      __libelf_seterrno (ELF_E_WRITE_ERROR);
+      size = -1;
+    }
+
   if (size != -1 && elf->parent == NULL)
     elf->maximum_size = size;