[PATCH] strip: Don't remove real symbols from allocated symbol tables.

[Mark Wielaard <mjw@redhat.com>]

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Having a symbol in an allocated symbol table (like .dynsym) that
points to an unallocated section is wrong. Traditionally strip
has removed such symbols if they are section or group symbols.
But removing a real symbol from an allocate symbol table is hard
and probably a mistake. Really removing it means rewriting the
dynamic segment and hash sections. Since we don't do that, don't
remove the symbol (and corrupt the ELF file). Do warn and set
the symbol section to SHN_UNDEF.

https://bugzilla.redhat.com/show_bug.cgi?id=1380961

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 src/ChangeLog |  5 +++++
 src/strip.c   | 35 ++++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index e5b3b20..70d11f2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2016-10-06  Mark Wielaard  <mjw@redhat.com>
+
+	* strip.c (handle_elf): Don't remove real symbols from allocated
+	symbol tables.
+
 2016-08-25  Mark Wielaard  <mjw@redhat.com>
 
 	* strip.c (handle_elf): Recompress with ELF_CHF_FORCE.
diff --git a/src/strip.c b/src/strip.c
index da093e9..819b67e 100644
--- a/src/strip.c
+++ b/src/strip.c
@@ -1341,15 +1341,12 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 
 		    /* Get the full section index, if necessary from the
 		       XINDEX table.  */
-		    if (sym->st_shndx != SHN_XINDEX)
-		      sec = shdr_info[sym->st_shndx].idx;
-		    else
-		      {
-			elf_assert (shndxdata != NULL
-				    && shndxdata->d_buf != NULL);
-
-			sec = shdr_info[xshndx].idx;
-		      }
+		    if (sym->st_shndx == SHN_XINDEX)
+		      elf_assert (shndxdata != NULL
+				  && shndxdata->d_buf != NULL);
+		    size_t sidx = (sym->st_shndx != SHN_XINDEX
+				   ? sym->st_shndx : xshndx);
+		    sec = shdr_info[sidx].idx;
 
 		    if (sec != 0)
 		      {
@@ -1387,6 +1384,24 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 			    shdr_info[cnt].shdr.sh_info = destidx - 1;
 			  }
 		      }
+		    else if ((shdr_info[cnt].shdr.sh_flags & SHF_ALLOC) != 0
+			     && GELF_ST_TYPE (sym->st_info) != STT_SECTION
+			     && shdr_info[sidx].shdr.sh_type != SHT_GROUP)
+		      {
+			/* Removing a real symbol from an allocated
+			   symbol table is hard and probably a
+			   mistake.  Really removing it means
+			   rewriting the dynamic segment and hash
+			   sections.  Just warn and set the symbol
+			   section to UNDEF.  */
+			error (0, 0,
+			       gettext ("Cannot remove symbol [%zd] from allocated symbol table [%zd]"), inner, cnt);
+			sym->st_shndx = SHN_UNDEF;
+			if (gelf_update_sym (shdr_info[cnt].data, destidx,
+					     sym) == 0)
+			  INTERNAL_ERROR (fname);
+			shdr_info[cnt].newsymidx[inner] = destidx++;
+		      }
 		    else if (debug_fname != NULL
 			     && shdr_info[cnt].debug_data == NULL)
 		      /* The symbol points to a section that is discarded
@@ -1394,8 +1409,6 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 			 this is a section or group signature symbol
 			 for a section which has been removed.  */
 		      {
-			size_t sidx = (sym->st_shndx != SHN_XINDEX
-					? sym->st_shndx : xshndx);
 			elf_assert (GELF_ST_TYPE (sym->st_info) == STT_SECTION
 				    || ((shdr_info[sidx].shdr.sh_type
 					 == SHT_GROUP)
-- 
1.8.3.1