[PATCH] core-dumping unreadable binaries via PT_INTERP

Proposed patch to fix #5 in
http://www.isec.pl/vulnerabilities/isec-0017-binfmt_elf.txt
aka
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-1073

To reproduce, do
* grab poc at the end of advisory.
* add line "eph.p_memsz = 4096;" after "eph.p_filesz = 4096;"
  where first "4096" is something equal to or greater than 4096.
* ./poc /usr/bin/sudo && ls -l

Here I get with 2.6.20-rc5:

 -rw------- 1 ad   ad   102400 2007-01-15 19:17 core
 ---s--x--x 2 root root 101820 2007-01-15 19:15 /usr/bin/sudo

Check for MAY_READ like binfmt_misc.c does.
Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/binfmt_elf.c

@@ -682,6 +682,15 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 			retval = PTR_ERR(interpreter);
 			if (IS_ERR(interpreter))
 				goto out_free_interp;
+
+			/*
+			 * If the binary is not readable then enforce
+			 * mm->dumpable = 0 regardless of the interpreter's
+			 * permissions.
+			 */
+			if (file_permission(interpreter, MAY_READ) < 0)
+				bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+
 			retval = kernel_read(interpreter, 0, bprm->buf,
 					     BINPRM_BUF_SIZE);
 			if (retval != BINPRM_BUF_SIZE) {

fs/binfmt_elf_fdpic.c

@@ -234,6 +234,14 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm,
 				goto error;
 			}
 
+			/*
+			 * If the binary is not readable then enforce
+			 * mm->dumpable = 0 regardless of the interpreter's
+			 * permissions.
+			 */
+			if (file_permission(interpreter, MAY_READ) < 0)
+				bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+
 			retval = kernel_read(interpreter, 0, bprm->buf,
 					     BINPRM_BUF_SIZE);
 			if (retval < 0)