[PATCH 2/2] libelf: Don't error out when sanity checking e_shoff if scncnt is zero.

[Mark Wielaard <mark@klomp.org>]

We won't use the e_shoff value in that case because we will set
elf->state.elf[64|32].scns.cnt to zero to indicate not to read
any section header data from the file.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libelf/ChangeLog   | 5 +++++
 libelf/elf_begin.c | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index 36b57dd..6aa1c6f 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,5 +1,10 @@
 2017-10-04  Mark Wielaard  <mark@klomp.org>
 
+	* elf_begin.c (file_read_elf): Skip sanity checking e_shoff if scncnt
+	is zero, we won't use it then.
+
+2017-10-04  Mark Wielaard  <mark@klomp.org>
+
 	* libelfP.h: Add ELF_E_INVALID_ELF to error values enum.
 	* elf_error.c (ELF_E_INVALID_ELF_IDX): New define. Use it as value
 	for ELF_E_INVALID_ELF in msgidx.
diff --git a/libelf/elf_begin.c b/libelf/elf_begin.c
index 5545278..fb3a5b5 100644
--- a/libelf/elf_begin.c
+++ b/libelf/elf_begin.c
@@ -373,7 +373,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
 	      || (((uintptr_t) ((char *) ehdr + e_shoff)
 		   & (__alignof__ (Elf32_Shdr) - 1)) == 0)))
 	{
-	  if (unlikely (e_shoff >= maxsize)
+	  if (unlikely (scncnt > 0 && e_shoff >= maxsize)
 	      || unlikely (maxsize - e_shoff
 			   < scncnt * sizeof (Elf32_Shdr)))
 	    {
@@ -475,7 +475,7 @@ file_read_elf (int fildes, void *map_address, unsigned char *e_ident,
 	      || (((uintptr_t) ((char *) ehdr + e_shoff)
 		   & (__alignof__ (Elf64_Shdr) - 1)) == 0)))
 	{
-	  if (unlikely (e_shoff >= maxsize)
+	  if (unlikely (scncnt > 0 && e_shoff >= maxsize)
 	      || unlikely (maxsize - e_shoff
 			   < scncnt * sizeof (Elf64_Shdr)))
 	    goto free_and_out;
-- 
1.8.3.1