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Date:      Wed, 13 Mar 2013 22:01:32 +0000 (UTC)
From:      Tijl Coosemans <tijl@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r248256 - head/sys/kern
Message-ID:  <201303132201.r2DM1WIT094803@svn.freebsd.org>
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Author: tijl
Date: Wed Mar 13 22:01:31 2013
New Revision: 248256
URL: http://svnweb.freebsd.org/changeset/base/248256

Log:
  - Fix two possible overflows when testing if ELF program headers are on
    the first page:
    1. Cast uint16_t operands in a multiplication to unsigned int because
       otherwise the implicit promotion to int results in a signed
       multiplication that can overflow and the behaviour on integer
       overflow is undefined.
    2. Replace (offset + size > PAGE_SIZE) with (size > PAGE_SIZE - offset)
       because the sum may overflow.
  - Use the same tests to see if the path to the interpreter is on the first
    page. There's no overflow here because size is already limited by
    MAXPATHLEN, but the compiler optimises the new tests better. Also fix an
    off-by-one error.
  - Simplify tests to see if an ELF note program header is on the first page.
    This also fixes an off-by-one error.
  
  Reviewed by:	kib
  MFC after:	1 week

Modified:
  head/sys/kern/imgact_elf.c

Modified: head/sys/kern/imgact_elf.c
==============================================================================
--- head/sys/kern/imgact_elf.c	Wed Mar 13 21:06:03 2013	(r248255)
+++ head/sys/kern/imgact_elf.c	Wed Mar 13 22:01:31 2013	(r248256)
@@ -661,9 +661,8 @@ __elfN(load_file)(struct proc *p, const 
 	}
 
 	/* Only support headers that fit within first page for now      */
-	/*    (multiplication of two Elf_Half fields will not overflow) */
 	if ((hdr->e_phoff > PAGE_SIZE) ||
-	    (hdr->e_phentsize * hdr->e_phnum) > PAGE_SIZE - hdr->e_phoff) {
+	    (u_int)hdr->e_phentsize * hdr->e_phnum > PAGE_SIZE - hdr->e_phoff) {
 		error = ENOEXEC;
 		goto fail;
 	}
@@ -743,7 +742,7 @@ __CONCAT(exec_, __elfN(imgact))(struct i
 	 */
 
 	if ((hdr->e_phoff > PAGE_SIZE) ||
-	    (hdr->e_phoff + hdr->e_phentsize * hdr->e_phnum) > PAGE_SIZE) {
+	    (u_int)hdr->e_phentsize * hdr->e_phnum > PAGE_SIZE - hdr->e_phoff) {
 		/* Only support headers in first page for now */
 		return (ENOEXEC);
 	}
@@ -762,8 +761,8 @@ __CONCAT(exec_, __elfN(imgact))(struct i
 		case PT_INTERP:
 			/* Path to interpreter */
 			if (phdr[i].p_filesz > MAXPATHLEN ||
-			    phdr[i].p_offset >= PAGE_SIZE ||
-			    phdr[i].p_offset + phdr[i].p_filesz >= PAGE_SIZE)
+			    phdr[i].p_offset > PAGE_SIZE ||
+			    phdr[i].p_filesz > PAGE_SIZE - phdr[i].p_offset)
 				return (ENOEXEC);
 			interp = imgp->image_header + phdr[i].p_offset;
 			interp_name_len = phdr[i].p_filesz;
@@ -1553,9 +1552,8 @@ __elfN(parse_notes)(struct image_params 
 	const char *note_name;
 	int i;
 
-	if (pnote == NULL || pnote->p_offset >= PAGE_SIZE ||
-	    pnote->p_filesz > PAGE_SIZE ||
-	    pnote->p_offset + pnote->p_filesz >= PAGE_SIZE)
+	if (pnote == NULL || pnote->p_offset > PAGE_SIZE ||
+	    pnote->p_filesz > PAGE_SIZE - pnote->p_offset)
 		return (FALSE);
 
 	note = note0 = (const Elf_Note *)(imgp->image_header + pnote->p_offset);

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